Effects of male plants with different ploidy on the fruit set and fruit characteristics in Actinidia arguta kiwifruit

Abstract:[Objective]In kiwifruit (Actinidia Lindl.),chromosome ploidy varies among species or cultivars.Both male and female kiwifruit cultivars have the diversity in the ploidy.The fruit setting rate and fruit characteristics of a female cultivar may be influenced by the pollen donors which are used to pollinate the flowers of the female.The objective of this study was to explore the effects of male plants with different ploidy on the fruit set and fruit characterstics in A.arguta kiwifruit and to offer instructions for choosing male plant.[Methods]'Ruby star'(Actinidia arguta) is an all-red female kiwifruit cultivar.In this study,' Ruby star' with tetraploid was pollinated by pollens from male plants with different ploidy including two diploid A.chinensis male selections('9-16' ♂,'2-69' ♂),one tetraploid A.chinensis male cultivar('Moshan4'),one tetraploid A.arguta male selection('11-17' ♂),one tetraploid A.arguta male cultivar(' Kuil(u) ♂),one hexaploid A.deliciosa male selection(' 6-20' ♂) and one hexaploid A.deliciosa male cultivar('Tomuri').The fruit setting rates of all combinations were investigated at 30 days after pollination.After harvest,characteristics of the fruits were evaluated including fruit weight,fruit- shape index,flesh color,soluble solids content,seed weight and seed number.[Results]When pollens of the two diploid A.chinensis male selections were used to pollinate 'Ruby star',the fruits fell down seriously with very low fruit setting rate(4.7%-6.1%).The fruit setting rates were nomal as expected following pollination by the tetraploid A.arguta male plants.When 'Moshan4'(a tetraploid A.chinensis male cultivar) was used as the pollen donor,the fruit setting rate of 'Ruby star' increased,but was 18.6%only.Fruits of 'Ruby star set well while their flowers were pollinated by Tomuri(a hexaploid A.deliciosa male cultivar) with fruit setting rate 52.4%- 86.3%which were close to the treatment when pollens of tetraploid A.arguta male plants were used.When Ruby star was pollinated by tetraploid A.chinensis or hexaploid A.deliciosa male plants,its fruit weight significantly decreased and the hue angle of fruit flesh also declined,which suggested that the fruits became smaller and the color intensity of flesh increased.When pollen of Moshan4(a tetraploid A.chinensis male cultivar) was used,both the fruit-shape index and soluble solids content of fruits significantly increased,while,the soluble solids content of fruits derived from pollination with pollen of Tomuri(a hexaploid A.deliciosa male cultivar) significantly decreased.Following pollination with tetraploid A.chinensis male plants,the number of developped seeds reduced and 1000-seed weight of seeds including developped seeds and undevelopped seeds significantly decreased.Following pollination by hexaploid A.deliciosa male plants,both the total number of seeds and the number of developped seeds significantly reduced.The 1000-seed weight was lighter than that of fruits derived from pollination with pollen of Kuil(u) ♂,but significantly weighed more than that of following pollination with pollen of 'Moshan4'.[Conclusion]Pollen donors with different ploidy affected the fruit set and fruit characteristics of 'Ruby star'.The fruit setting rate of 'Ruby star' significantly decreased with rate 4.7%-6.1%which couldn t meet the demands of the production when diploid A.chinensis males were used as pollen donors.When the tetraploid A.chinensis male 'Moshan4' was used,the fruit setting rate slightly increased,but was still low with rate 18.6%.When the hexaploid A.deliciosa male was used to pollinate the flowers of 'Ruby star',the fruit setting rate was similar to that tetraploid A.arguta male plant caused,with a high rate 86.3%.It was suggested that 'Ruby star' set well in the intraspecies intraploidy crosses as expected.Besides the tetraploid A.arguta males,male plants at higher ploidy levels than the female,such as hexaploid A.deliciosa males could be chosen to pollinate ' Ruby star' to obtain a high fruit setting rate.Moreover,the effects of pollen donors on fruit weight,flesh color and seed weight of 'Ruby star'tended to be associated with the ploidy level of males.Following pollination with tetraploid A.chinensis and hexaploid A.deliciosa male plants,the fruit weight significantly decreased and the hue angle of fruit flesh also declined.1000-seed weight of the seeds in the fruits from pollination by the tetraploid A.arguta male ' Kuil(u)' ♂ tended to weigh more than those from pollination by the hexaploid A.deliciosa male ' Tomuri which weighed more than those from pollination by the tetraploid A.chinensis male Moshan4.