HortJ

Parthenocarpic apple cultivars have been recognized with simultaneous homeotic floral organ mutations. The mutations included replacements of petals to sepals and stamens to carpels, which were same as the class B mutations of floral organs from Arabidopsis and snapdragon. For apple, the parthenocarpy and class B mutations were tightly inherited and MdPISTILLATA (MdPI) gene deficiency caused homeotic mutations. However, the relationship between the suppression of MdPI and parthenocarpy was unclear. Transgenic apples with suppressed MdPI expression using an anti-sense or co-suppression method were found to have the same homeotic floral organ mutations as parthenocarpic cultivars. Further, the transformants with co-suppression showed parthenocarpy and overexpression of MdPI in fruits prevented normal fruit growth. Other apple MADS genes were analyzed for parthenocarpy. MdMADS13 is classified as another class B gene, which plays a role in floral organ formation together with MdPI. In addition, MdMADS1/8 and MdMADS9 are classified as class E genes, which are could function like SEP1 and 2 genes from Arabidopsis. The MdMADS1/8 and MdMADS9 gene-suppressed apple transformants showed strong inhibition of fruit enlargement, supporting the idea that MdMADS1/8 and MdMADS9 contribute to hypanthium development. It is possible that the MdPI, MdMADS13, MdMADS1/8, and MdMADS9 proteins formed a heterotetramer as a transcriptional regulator and were involved in fruit development. Other plant species such as tomato and grape also showed the respective class B genes affected fruit development. The suppression of tomato class B genes led to class B floral organ mutations and parthenocarpy, and a grape mutant with class B gene expression ectopically inhibited fruit flesh development. Both class B genes seemed to prevent fruit development similar to the apple MdPI. This suggests that the class B genes play not only a role in forming the identities of petals and stamens, but also a pivotal role in fruit development.

Pollination is an important factor affecting fruit development in highbush blueberry (Vaccinium corymbosum L.). In general, planting several different blueberry cultivars increases the chances of cross-pollination and ensures high-quality fruit production. However, little is known about the effects of the pollen source on fruit development in blueberry. The aims of this study were: 1) to understand the effects of the pollen source on fruit size and quality; and 2) to explore the mechanisms underlying fruit development affected by the pollen source. We first characterized the pollination effect on fruit development using 14 different pollination combinations for several years and found that the number of mature seeds and fruit size differed significantly among the fruit pollinated by different pollen sources. Significant correlations between the number of mature seeds and fruit size were found in most combinations, whereas the number of mature seeds was not correlated with other fruit quality parameters such as sugar concentration. Our results and those of previous reports showed that the number of mature seeds, which was influenced by the pollen source, was a primary determinant of fruit size. Time-course observation during fruit development revealed that fruit weight and cell size significantly differed between self-pollinated and cross-pollinated fruit from 30 days after pollination onwards. To explore the molecular mechanisms underlying berry growth affected by developing seeds, we compared gene expression changes between self-pollinated and cross-pollinated fruit. Transcriptome analysis of fruit at 10 days after pollination suggested that auxin signaling pathways were enhanced in cross-pollinated fruit compared with self-pollinated fruit. We thus hypothesize that activated auxin signal transduction underlying early stage seed and fruit development may promote fruit cell enlargement during the early stage of fruit growth in highbush blueberry.

In protected agriculture, optimum temperature management is crucial for enhancing fruit productivity and maintaining cost-effective production. The aim of the present study was to investigate the effects of temperature on peach fruit development and quality. Container-grown ‘KU-PP2’ peach trees grafted on low-chill peach rootstocks were cultivated under controlled conditions at different temperatures (20, 25, and 30°C) during fruit development for two years (2020 and 2021). Fruit growth rates were calculated by measuring fruit diameter every 3 d from fruit setting to first harvest; fruit quality and phytochemistry were analyzed at harvest. Growing temperature markedly affected fruit growth, maturation, and fruit quality. The development of fruit in all treatments exhibited double sigmoid growth curves that included three stages (S1, S2, and S3). Fruit growth rate during S1 and S2 stages was increased, and fruit development period was significantly shortened with an increase in temperature. Contrary to the duration of S3, which was longer at higher temperatures, fruit grown at a high temperature (30°C) ripened by 12–18 days earlier than those grown at low-temperature regimes. In addition, high-temperature conditions were also associated with reduced fruit quality (size, weight, and sweetness), but enhanced development of red coloration. Therefore, even though high-temperature conditions can accelerate early fruit expansion and hasten fruit maturity, such conditions also have negative effects on important agronomic fruit traits.

Gibberellins are widely used to induce seedlessness in table grape production, but are not effective for every cultivar or developmental stage. In order to characterize the potential physiological mechanism behind gibberellin-induced seedlessness, we conducted tissue-specific transcriptome analysis of ovules and ovaries from cultivars with different levels of receptiveness to seedlessness induction. GA₃ treatment at full bloom highly induced gibberellin signaling and various phytohormone signaling pathway genes in ovules at two days after treatment, but had less effect in ovaries, which suggests that GA₃ directly affects seed development. During the development to six days after GA₃ application, cell cycle-related genes in the ovules were markedly downregulated, indicating that this may be related to ovule abortion induction. The marked transcriptomic responses were largely absent in a cultivar with low receptiveness to gibberellin-induced seedlessness, suggesting a crucial role for the observed tissue-specific responses in the successful induction of seedlessness by GA₃ application. Collectively, our transcriptome analysis highlights distinct tissue-specific reactions to GA₃ during early berry development, providing important insights for the successful production of seedless berries by gibberellin application.

The Chinese cherry (Prunus pseudocerasus/Cerasus pseudocerasus), which is native to China, is an economically important tetraploid fruiting cherry species. Its industry has been greatly limited due to some general disadvantages in the fruits such as small fruit size, high acid content, and short shelf-life. As such, it is urgent to carry out cross breeding and genetic improvement of this species. Here, seven cross combinations were designed by selecting five genotype landraces of the Chinese cherry and one semi-wild resource as cross parents. The fruit-set percentage, germination rate of the hybrid seeds, and growth status of the F₁ seedlings varied among different parental genotypes and cross combinations. Three or four S-genotypes were detected in six tetraploid parents, with a maximum of five different alleles between two parents. Both the pollen vigor of the male parent and the differential S-genotype between parents may contribute to the variation in fruit-set percentages, ranging from 0 to 28.55%. Significant differences in the F₀ fruit traits were observed among different combinations, indicating potential metaxenia of the Chinese cherry. Appropriate pretreatments, including the removal of endocarps, soaking with 150 mg/L GA₃ for 24 h, and chilling stratification for 7–10 days, could significantly increase the germination rate of the hybrid seeds. According to the overall performance, using (semi)-wild resources as one of the parents should be taken into consideration more in Chinese cherry breeding programs. On the basis of these findings, we further constructed a flow chart for successful intra-specific crossing and efficient cultivation of robust F₁ seedlings. This study will provide important references for the selection of cross parents, establishment of a feasible breeding program, and cultivation of robust F₁ progenies of the Chinese cherry.

Low temperature negatively affects pollen germination in many species, but artificial pollination can help alleviate these negative effects. With ongoing environmental changes, it is important to select pollinizers with pollen that has superior germination properties at lower temperatures. To select candidate cultivars for a new Pyrus pollinizer for pollen with superior germination properties at low temperatures, in vitro pollen germination was studied in 129 Pyrus plants. The highest germination percentage for most Pyrus plants was observed at 25.0°C and was < 20% at 10.0°C. However, ‘Narayoshinokoboku’, ‘Imamuranatsu’, and ‘Tosanashi’ showed a higher germination rate than the other Pyrus plants at 10.0°C, and the germination percentage rates of three plants were > 30%. The fruit setting percentage of the cultivars ‘Kosui’, ‘Hosui’, and ‘Gold-Nijisseiki’ were > 85% by pollination using these three selected cultivars in an open field. In addition, S-genotyping in selected cultivars was determined as follows: ‘Tosanashi’ (S₁S₇), ‘Imamuranatsu’ (S₁S₁₂), and ‘Narayoshinokoboku’ (S₁S₉). From these results, we concluded that all three cultivars showed cross-compatibility in most pear cultivars of the four major Japanese pear cultivars. The percentage of flower bud formation in ‘Tosanashi’ was > 50%, and the amount of pollen from ‘Narayoshinokoboku’ was more than double the amount of ‘Chojuro’. By assessing the chilling requirement in selected cultivars, a safe area for growth for each cultivar was evaluated as all areas with the exception of the Kyushu and Shikoku regions, based on the ongoing progress of global warming (average daily temperature increase of 3.7°C). In conclusion, we selected ‘Narayoshinokoboku’ and ‘Tosanashi’ as new Pyrus pollinizers because they combine the advantages of low-temperature germinability and high pollen load.

This study was conducted to obtain insights into unreduced gamete formation in Citrus tamurana hort. ex Tanaka ‘Nishiuchi Konatsu’ and ‘Hyuganatsu’, inferred from unreduced pollen and egg cell genotype information. To establish a method for fine genotyping of tissues with higher ploidy levels (up to hexaploidy), we first identified heterozygous single-nucleotide polymorphism (SNP) markers (CiC4240-04 and CiC5327-03) with close genetic distance to centromeres of ‘Nishiuchi Konatsu’ and ‘Hyuganatsu’. Fluorescence intensity-based standard plots were generated using real-time qPCR to accurately genotype these SNP markers on a two-dimensional panel. Ten normal seeds were obtained from fertilization of unreduced gametes by self-pollination of ‘Nishiuchi Konatsu’ or ‘Hyuganatsu’ × ‘Nishiuchi Konatsu’ crosses. Inner seed coats with hexaploid endosperm tissues and tetraploid embryos were obtained from normal seeds, and their CiC4240-04 and CiC5327-03 genotypes were determined with standard plots using real-time qPCR. Genotypes of unreduced pollen and egg cells were uniquely determined from the genotype information of 6x endosperms and 4x embryos, and the unreduced gamete formation process was inferred. The results showed that unreduced pollen formation was almost entirely due to first division restitution (FDR); therefore, it was concluded that FDR was the dominant formation process for unreduced pollen in ‘Nishiuchi Konatsu’. In contrast, there was no dominant process for the formation of unreduced egg cells because both FDR and second division restitution occurred in almost the same number of individuals with unreduced egg cells.

Large nut weight (NW) is an important target in chestnut breeding. The present study was conducted at the Nakatsugawa branch of the Gifu Prefectural Research Institute for Agricultural Technology, an important chestnut breeding site in Japan. We estimated the environmental variance components for NW by using nine cultivars/selections with three single-tree replicates for six years. The number of nuts evaluated for each tree was mostly over 100 nuts, with an average of 440 nuts. Subsequently, the dataset of average NW values for each tree was log-transformed and analyzed by ANOVA. The effects of genotype, year, and the genotype × year interactions were highly significant, whereas the tree effect was negligible. The resulting environmental variance components for the log-transformed values were as follows: variance among years = 5.2 × 10⁻⁴, variance among trees within genotype = 0, variance associated with the genotype × year interactions = 7.6 × 10⁻⁴, and residual variance = 11.2 × 10⁻⁴. The results suggest that tree replication is not necessary to evaluate the genotypic value of cultivars/selections or offspring in breeding and that year effect adjustment and yearly repeated measurements can effectively reduce environmental variance. The NW of 27 cultivars/selections with potential as cross-parents was also estimated with no tree replications and via measurements repeated for three years; the results ranged from 10.7 to 47.4 g, with high broad-sense heritability (0.93) based on a three-year evaluation for the log-transformed data. Based on the environmental variance estimates, the cultivars/selections used in chestnut breeding with NW above 22.3 and 26.7 g should be selected by evaluating one tree for three years at 95% probability and selecting those having nuts of 25 and 30 g or more, respectively.

Seed size affects the edible portion rate of lychee fruit and is therefore an important trait for fruit quality in lychee (Litchi chinensis). Lychee fruits can be classified into four categories in terms of seed properties: normal, small, aborted seed and seedless. ‘Salathiel’ is known to bear a relatively high rate of aborted-seeded (pseudo-parthenocarpy, stenospermocarpy) and seedless (parthenocarpy) fruit regardless of environmental and cultivation conditions. In other horticultural fruit crops, such as tomato, auxin metabolism and signaling is critical for parthenocarpy, although auxin metabolism has not been characterized in relation to (pseudo) parthenocarpy in lychee. The purpose of this study was to characterize the physiological and morphological properties of maternal reproductive organs in ‘Salathiel’ female flowers, with a specific focus on the associated auxin metabolism. Microscopic observations of the internal structures of the ‘Salathiel’ embryo revealed that ‘Salathiel’ reproductive organ differentiation is similar to that of normal-seeded cultivars. However, the obturator was significantly smaller in ‘Salathiel’ than in other normal-seeded cultivars, suggesting that specific developmental characteristics may exist in the maternal reproductive organs of ‘Salathiel’. Our investigation of indole acetic acid (IAA) contents revealed that IAA levels were significantly higher in ‘Salathiel’ than in other cultivars. Moreover, the IAA metabolite contents also differed significantly between ‘Salathiel’ and the normal-seeded and small-seeded cultivars. Specifically, N-3-hydroxy-2-oxindole-3-acetyl glutamic acid contents were significantly higher in ‘Salathiel’ than in ‘Yu Her Pau’ and ‘Hei Ye’. 3-hydroxy-2-oxindole-3-acetic acid was lower in ‘Yu Her Pau’ and ‘Salathiel’ than in ‘Hei Ye’, while indole-acetylaspartic acid was significantly lower in ‘Salathiel’ compared to ‘Hei Ye’. Expression analyses of the genes related to auxin biosynthesis, catabolism, transport, and signaling indicated that the IAA influx-related and efflux-related gene expression levels were respectively higher and lower in ‘Salathiel’ than in the other cultivars, which is consistent with the increased IAA accumulation in the ‘Salathiel’ ovary. The possible involvement of auxin metabolism in the aborted-seeded and seedless fruit production in ‘Salathiel’ is discussed herein.

Changes in anthocyanin and endogenous abscisic acid (ABA) contents in the berry skins of Vitis labruscana × V. vinifera cultivars, ‘Aki Queen’, and ‘Ruby Roman’ were investigated during the fruit development period. Color development of ‘Aki Queen’ berries mainly occurred within 20 days post véraison, while that of the ‘Ruby Roman’ was prolonged for about 40 days. In both cultivars, the ABA level in the berry skin started to increase a few days before véraison; however, ABA accumulation ceased approximately 10 days after véraison in ‘Aki Queen’, while it continued until the late stage of maturation in ‘Ruby Roman’. In addition, higher indole-3-acetate aspartate (IAA-Asp) and lower isopentenyladenine (iP) contents were observed in ‘Ruby Roman’ than in ‘Aki Queen’ at the late development stage. The expression analysis of genes involved in ABA metabolism revealed that V. vinifera 9-cis-epoxycarotenoid dioxygenase 3 (VviNCED3), which is assumed to play a major role in ABA biosynthesis, remained relatively higher in ‘Ruby Roman’ than in ‘Aki Queen’ after véraison. Considering that ABA plays a regulatory role in grape maturation, these results may indicate that the coloration of ‘Ruby Roman’ at the later stage of maturation is partly attributable to an increased ABA pool in berry skins.

Akebia trifoliata is cultivated locally in few areas of Japan. Artificial pollination is considered indispensable for stable fruit production, as Akebia spp. exhibit self-incompatibility (SI). However, little is known about the reproductive physiology required for effective artificial pollination. In this study, we investigated the effects of self-pollen contamination on the fruit set of ‘Fuji Murasaki’ (A. trifoliata), one of the main lines in Yamagata Prefecture, Japan. Both the self- and cross-pollen tubes reached the base of the ovary and penetrated the ovules at 10 days after pollination, indicating that A. trifoliata exhibits late-acting SI. Self-pollination one day before cross-pollination completely inhibited fruit set, while self-pollination one day after cross-pollination did not inhibit fruit set in both 2016 and 2020, indicating interference in cross-pollination by self-pollen contamination. Fruit set rates for artificial pollination using a 1:1 mix of self- and cross-pollen were significantly lower than those that used non-contaminated cross-pollen in both 2016 and 2019, but were comparable when using a 1:1 mix of lycopodium powder and cross-pollen. The seed number of fruit resulting from mixed pollination was not significantly lower than that of fruit resulting from cross-pollination. Interestingly, 1:1 mixed pollination of self- and cross-pollen sometimes yielded abnormal fruits with an apex that remained pale and did not soften. These results suggest that excessive self-pollen contamination in artificial pollination may not be desirable for A. trifoliata fruit production.

Prunus (Rosaceae) includes many commercially important fruit crop species that exhibit self-incompatibility (SI), including sweet cherry (P. avium L.), Japanese apricot (P. mume Sieb. et Zucc.), Japanese plum (P. salicina Lindl.), apricot (P. armeniaca L.), and almond (P. dulcis [Mill.] D. A. Webb.). These species exhibit S-ribonuclease-based gametophytic SI, which prevents self-pollen tube growth in the pistil. The successful production of self-fertilized progeny accomplished by artificially overcoming the SI barrier has not been reported in Prunus, but self-compatible (SC) Prunus mutants with mutated pollen S determinant S haplotype–specific F-box (SFB) or pollen modifier M-locus encoded glutathione S-transferase-like (MGST) genes have been identified and used as SC cultivars and breeding stocks. In this study, we suppressed translation of SFB or MGST mRNA in self-pollen using antisense oligonucleotides to overcome the SI barrier in P. avium, P. mume, and P. salicina. Over the three years of the study, we obtained self-fertilized progeny of SI Japanese plum ‘Sordum’ only when SFB or MGST was knocked down. We also found that the average length of the self-pollinated pollen tube in the pistil of ‘Sordum’ was increased following treatment with an antisense oligonucleotide against SFB. This is the first report regarding the successful production of selfed progeny of Prunus obtained by disrupting SI. Our findings also provide evidence that the loss of function of SFB or MGST in Prunus pollen leads to SC.

To determine the effects of drought stress, especially light drought stress, on flower number in passion fruit, one-year-old passion fruit plants grown in 7.5 L plastic pots were subjected to different soil water content treatments, namely wetness, light drought, and heavy drought for two months. Average, maximum, and minimum soil water contents (v/v) were 44, 47, and 41% in the wetness treatment, 23, 40, and 11% in the light drought treatment and 11, 33, and 6% in the heavy drought treatment. Flower number decreased as the strength of drought stress increased, although the number of nodes and flower buds did not. Flowering periods were from June 27 to July 19 in the wetness treatment and June 26 to July 16 in the light drought treatment with three peaks around July 1, 6, and 13. In the heavy drought treatment, the flowering period was from July 11 to 18 with one peak. The flower bud number was not affected by drought stress. Light drought stress did not suppress vegetative growth, such as vine length, leaf number, leaf length, or photosynthetic rate, although heavy drought stress did. Stomatal conductance was suppressed by light drought only at 12:00PM and by heavy drought throughout the day. Leaf water potential was decreased by heavy drought at 3:00PM, but not by light drought. In the wetness and light drought treatments, visible wilting was not observed, and in the heavy drought treatment the plants wilted before irrigation, although they recovered about 15 min after irrigation. In conclusion, even light drought stress, which did not suppress vegetative growth, reduced the flower number in passion fruit. Drought stress suppressed flower bud development but not differentiation.

Self-incompatibility in Citrus species is an important trait related to fruit set and seed formation. In particular, self-incompatible citrus varieties combined with sufficient parthenocarpy produce seedless fruits. The characteristics of self-incompatibility have been studied for many years, and essential traits, such as pollen tube elongation behavior and self-incompatibility genotypes, have been characterized. Recently, it has been shown that the genetic mechanism of self-incompatibility in citrus varieties is S-RNase-based gametophytic self-incompatibility. To date, 18 S-RNases (17 self-incompatible alleles and 1 self-compatible allele) have been identified. The DNA markers for S-RNases can enable the early identification of self-incompatibility/compatibility status. The expression of self-compatibility in Citrus species is ascribed to the presence of the self-compatibility S_m allele, which is a defective S-RNase, and to the suppression of S-RNase expression. Polyploidization induces self-compatibility in Citrus species: Citrus tamurana ‘Hyuganatsu’ is substantially self-incompatible; however, its bud mutation, ‘Nishiuchi Konatsu’, is self-compatible. ‘Nishiuchi Konatsu’ is diploid; however, it forms unreduced pollen, which causes the breakdown of self-incompatible reaction when self-pollinated because of a competitive interaction within the same individual. In addition, after fertilization by unreduced pollen, seed formation is also inhibited by triploid block caused by interploid hybridization between diploid pollen and haploid egg cells. Therefore, ‘Nishiuchi Konatsu’ shows self-compatibility regardless of the self-incompatibility haplotype and produces fruits with few seeds. The seedlessness trait could be beneficial for citrus breeding in the future; however, the genetic mechanisms involved in the expression of this trait remain unclear. This review focuses on the recent advances in the genetics of self-incompatibility in citrus plants, implicating the mechanisms involved in self-incompatibility and their applications for achieving the desired trait of seedlessness in citrus fruits.

The development of intergeneric hybrids for horticultural crops has been attempted to introduce new quality and resistance traits and to enlarge the gene pool. Interspecific and intergeneric hybridization are often hindered by incompatibility reactions occurring at various stages of hybridization, from early pollination to initial growth, and the reproductive stages of the progeny. In this study, we investigated intergeneric and interspecific cross-compatibility among six species in the tribe Maleae (Rosaceae), namely, Pyrus communis (European pear), P. pyrifolia (Japanese pear), Malus × domestica (apple), Eriobotrya japonica (loquat), Cydonia oblonga (quince), and Pseudocydonia sinensis (Chinese quince). In vivo pollen tube growth tests showed the presence of a postmating, prezygotic barrier in many cross-combinations, in which cross-compatibility was regulated by both genetic distance and crossing direction. Strong hybridization barriers were observed in pollen tube growth and fruit setting when intergeneric hybridization was performed with E. japonica, a species phylogenetically distant from the others studied. Different compatibility reactions in reciprocal crosses were observed in some intergeneric hybridizations; C. oblonga as a pollen donor was incompatible with P. sinensis, whereas the reciprocal cross was compatible, resulting in the development of hybrid seedlings. Furthermore, the pollen tube growth rate differed among Pyrus species when pollinated on the apple pistils, suggesting divergence of cross-compatibility response in a specific linage. Factors affecting intergeneric hybridization are discussed with reference to the genetic distance between species and morphological characteristics such as pistil length. Our comprehensive assessment of intergeneric cross-compatibility will help provide a way to overcome crossing barriers and develop new hybrid crops in the tribe Maleae.

The aim of this study was to select new pollinizers for Prunus spp. with high pollen germination rates at low temperatures and assess their effect on the fruit set of Japanese plum cultivars. In this study, we examined in vitro pollen germination in 17 plum cultivars and two Myrobalan plum lines (420-2-2 and 421-3-1) at eight temperatures (7.5°C, 10.0°C, 12.5°C, 15.0°C, 17.5°C, 20.5°C, 22.5°C, and 25.0°C). The extent of pollen germination was affected by the incubation temperature. The germination rates of most cultivars were highest between 20.0°C to 25.0°C and ≤ 20% between 7.5°C to 10.0°C. However, the two Myrobalan plum lines (420-2-2 and 421-3-1) showed higher germination rates than the other cultivars at 10.0°C with ≥ 25% germination. The high germination rate in Myrobalan 420-2-2 was further confirmed in experiments conducted by our group in 2020. Open field studies on the Japanese plum ‘Kiyo’ revealed that the fruit setting rate was 17.6% using Myrobalan 420-2-2 and only 9.9% in the control using ‘Hollywood’. The fruit setting rate of the Japanese plum ‘Taiyo’ was approximately 20% when pollinated with both the cultivars. However, both fruit setting rate and fruit quality did not differ significantly between ‘Kiyo’ and ‘Taiyo’ with either pollination treatment. The formation rates of perfect seeds in ‘Taiyo’ were 90% and 65% by pollination using Myrobalan 420-2-2 and ‘Hollywood’, respectively. However, pollination treatment using pollen from both cultivars did not show any variations in the early development of the ovary and ovule. S-genotyping in Myrobalan 420-2-2 was determined as S₇S₁₀; therefore, we assumed that Myrobalan could be cross-compatible with many other plum cultivars. In conclusion, we selected Myrobalan 420-2-2 as a new plum pollinizer as it can effectively pollinate Japanese plum and germinate at low temperatures with no adverse effect on fruit set and quality.

Based on hand pollination, 217 crabapple cultivars were examined to determine their self-fruitfulness potential. One hundred and six cultivars failed to self-pollinate for fruits set. More than 50% self-pollinated fruit were obtained from 29 cultivars. Especially, the fruit set of ‘Jiringo’, ‘Karafutozumi’, ‘Katherine Crab’, Malus hupehensis, M. scheideckeri, ‘Mary Porter Crab’, ‘Mokoto’, ‘Nepal Apple Collections No. 85-I-74-3 86090-3’, ‘Scheidecker Crab’, ‘Silver Moon Crab’, ‘Tachikaido’, and ‘Tea Crab 81105’ were more than 50% by self-pollination over two years. ‘Jiringo’, ‘Katherine Crab’, ‘Mary Porter Crab’, ‘Scheidecker Crab’, and ‘Tachikaido’ have the potential to be self-compatible cultivars because their self-pollinated fruits contain complete seeds. Non-pollinated fruits of M. scheideckeri, ‘Nepal Apple Collections No. 85-I-74-3 86090-3’, and ‘Tea Crab 81105’ may contain apomictic seeds. Moreover, self-pollinated fruits contained seeds and non-pollinated fruits contained no seeds, suggesting that ‘Karafutozumi’ and ‘Mokoto’ may be self-compatible and parthenocarpic. The study findings not only provide breeding material for self-compatible apple cultivars, but also have led to the discovery of new apomictic and parthenocarpic research materials.