Evaluation on fruit quality characteristics and identification at molecular level of distant hybrids Ganjin and Ganhong

Abstract：【Objective】Based on the measurement of physiological indexes in the field and InDel molecular markers, the fruit quality characteristics of the superior variety Ganjin and excellent line Ganhong from the distant hybridization between apple and pear were evaluated and the authenticity of the hybrids was determined by specific molecular markers, which could provide a theoretical basis for the research on the resistance breeding of the late true hybrid.【Methods】The growth potential and fruit economic traits of hybrids Ganjin and Ganhong were analyzed. The Ganjin apple was bred between Red Delicious as the female and the Apple pear as the male. In May 1974, conventional hybridization was carried out, 131 flowers were hybridized, 5 fruits set, 5 fruits were picked and 16 full seeds were obtained. In 1975, 12 seeds were sown, 8 seeds germinated and 5 seedlings were survived finally. In 1979, the spring branch was top-grafted on the mature Ralls apple tree. In 1981, the fruit tree blossomed and bore fruit. In 1987, the best line (originally coded as 7403-03) was selected. In 1990, it was identified and formally named as Ganjin. Ganhong apple was bred between Golden Delicious as the female and Clapp’s Favorite as the male. In May 1975, conventional hybridization was carried out, 120 flowers were hybridized, 7 fruits set, 6 fruits were picked, and 20 full seeds were obtained. In 1975, 16 seeds were sown, 10 seeds germinated and 8 seedlings survived finally. In the spring of 1979, the branch was top-grafted on the Ralls apple tree. In 1981, the fruit tree blossomed and bore fruit, and in 1987, the bestline (originally coded as 7504-01) was selected. In 1990, it was tentatively named Ganhong. The longitudinal and transverse diameters of fruit were measured with a vernier caliper. The single fruit weight was weighed with an electronic balance, the fruit firmness was measured with the GY-1 firmness tester, and the soluble solids content was measured with the WYT-A handheld sugar meter. The genome sequence of Golden Delicious apple was compared with that of European pear (Pyrus communis L.) Bartlett pear. The genome sequence of extracted apple could not be compared with that of European pear and the genome sequence of European pear could not be compared with that of apple. The specific sequences extracted were filtered and the specific sequences with a length of 100-500 bp were selected. The specific sequences were compared again in the apple and pear genomes to verify their specificity. Specific sequences of apple and pear genomes were obtained, specific fragments of 100-250 bp size were selected, and the DNA of the hybrid and parent was amplified by designing intergeneric specific primers through Primer 5.0.【Results】The growth potential of Ganjin and Ganhong was vigorous, with strong stress resistance and good fruit quality. The internode length of Ganjin branches was 2.3 cm, and the bud break rate was 79.1% . The axillary flower buds accounted for 12.5% , the flower buds had strong cold resistance, and the fruit set rate per cluster was 80%. The average fruit weight was 220 g, the fruit shape index was 0.88, the fruit firmness was 8.5 kg · cm- 2 , and the soluble solids content was 15.8%. The internode length of Ganhong was 2.6 cm, and the bud break rate was 5.1%. The axillary flower buds reached 16.5%, the flower buds also had strong cold resistance, the fruit set rate per cluster reached 76%. The average fruit weight was 200 g, the fruit shape index was 0.85, the fruit firmness was 8.2 kg · cm-2 , the soluble solids content was 15.2%. The Ganhong fruit has delicious sweet and sour flavor and strong fragrance. Primers were designed from specific fragments of pear and apple, and specific primers that could amplify specific bands only in pear or apple were screened. Due to the specificity of some primers in the trial or the discomfort of the reaction system, 6 pairs of specific primers were finally selected: M1, M2, M3, P1, P2 and P3. The specific primers M1, M2 and M3 only amplified bands in maternal apple variety, but not in male pear. The three primers consisting of P1, P2 and P3 could only amplify bands in male pear variety, but could not amplify bands in apple. Two pairs of universal primers U1 and U2 can amplify bands in both apple and pear, which can repeat 3 times, that is, apple and pear can be clearly distinguished. In addition, when apple M1, M2 and M3 and pear P1, P2 and P3 primers amplified the hybrid progenies Ganjin and Ganhong, they all showed bands, indicating that the hybrid progeny had both apple and pear genes.【Conclusion】In this study, the specific primers between pear and apple developed by gene specific molecular markers were used to identify the authenticity of distant hybrids, which could provide a valuable reference for the identification of distant hybrids between apples and pears as well as other fruit crops.