Study on the inheritance of fruit color in loquat based on PSY gene marker

Abstract:【Objective】Loquat (Eriobotrya japonica Lindl.), a genus of flowering plants in the Rosaceaefamily, has been cultivated in China more than 2 000 years. The carotenoid is the main pigment in loquatfruit, which leads to a difference in flesh color. Traditionally, loquat cultivars can be divided intotwo groups based on its flesh colors, that is, yellow-flesh and white-flesh. Compared with yellow-fleshcultivars, white-fleshed cultivars have become more popular because of their delicious flesh and highereconomic value, and breeders also prefer to breed new white-flesh cultivars. However, the genetic mechanismof loquat flesh color is still unclear. Loquat breeding is limited at the seedling selection stage becauseof the long juvenile period. Therefore, it is very important to study the genetic inheritance of loquatflesh color. In this study, we analyzed the flesh color segregation ratio of different crossing combinationsin order to study the genetic inheritance of loquat flesh color. Flesh color specific molecularmarkers were used to identify the flesh color of hybrid progenies at seedling stage. 【Methods】Based onthe specific molecular markers of loquat flesh color, there are two types of molecular markers in yellowfleshloquat cultivars: some yellow-flesh cultivars possess a long amplified fragment (1 013 bp), somepossess two amplified fragment: a long fragment (1 013 bp) and a short fragment (319 bp) . However, all white-flesh cultivars possess only a short amplified fragment (319 bp). Therefore, two types of yellow-flesh cultivars‘Meihuaxia’and‘Zaozhong No. 6’and one white-flesh cultivar‘Baiyu’were selectedas parent materials in this study. Field crossing and selfing were carried out in 2017, and a totalof 9 progeny populations were created, including 6 cross combinations and 3 selfing combinations.Among these progeny populations, the largest combination was‘Baiyu’בMeihuaxia’, the number ofoffsprings were 153; the small estprogeny came from the selfing of‘Meihuaxia’, the number of offspringswere 110. After sowing and seedling, the genomic DNA of each single plant of the 9 hybridcombinations was extracted and the RAPD and SRAP molecular markers were used to identify the trueand false hybrids of the offspring. We found that 10 RAPD primers, 9 SRAP forward primers and 11 reverseprimers could be used for further identification. Altogether 1166 offspring individuals werescreened as true hybrids by RAPD and SRAP molecular markers and the average true hybrid rate was91.35%. The flesh color of each offspring of 9 progeny populations was identified using loquat fleshcolor specific DNA molecular markers at seedling stage, and their genetic inheritance was also investigated.Chi- square test was used to test whether the separation ratio of flesh color was in accordancewith Mendelian’s law of heredity.【Results】The fruit flesh color segregation rations were different indifferent hybrid combinations. The hybrid combinations‘Meihuaxia’בBaiyu’and‘Baiyu’בMeihuaxia’didnot show segregation in flesh color, the flesh color of their offsprings were all identified asyellow. The same results appeared in the hybrid combinations‘Meihuaxia’בZaozhong No. 6’and‘Zaozhong No. 6’בMeihuaxia’, their offsprings were all identified as yellow- flesh. However, theflesh color was obviously separated in the hybrid combination of‘Zaozhong No. 6’בBaiyu’and‘Baiyu’בZaozhong No. 6’, the separation ratios of yellow flesh and white flesh were 1:0.89 and 1:0.87, respectively. Their separation ratio was in accordance with Mendelian's law of heredity. In thethree selfing progenies of‘Meihuaxia’and‘Baiyu’there was no segregation on fruit flesh color, alloffsprings of‘Meihuaxia’selfing were identified as yellow-flesh and all offsprings of‘Baiyu’selfingwere identified as white-flesh. But, in selfing progeny of‘Zaozhong No.6’, the segregation ratio of yellowand white flesh was 2.94∶1, and its separation ratio wass also in accordance with Mendelian’s lawof heredity.【Conclusion】For the first time, we used specific DNA molecular markers to study the separationof loquat flesh color from 9 different hybrid combinations. Our results showed that loquat fleshcolor was controlled by a pair of allel. The yellow flesh trait was dominant and white flesh trait was recessive.By the way, we could further distinguish the homozygous or heterozygous state of loquat yellowflesh trait using specific DNA molecular markers, the genetype of yellow-flesh was homozygouswhen the amplified band was a single long fragment (1 013 bp) and the DNA molecular markers weretwo amplified fragments (1 013 bp and 319 bp). The genotype of yellow-flesh was heterozygous. Theseresults can provide a theoretical basis for the breeding of new loquat cultivars, especially for the breedingof the new white-flesh loquat cultivars.