DERIVATIVES OF VACCINIUM-ARBOREUM X VACCINIUM SECTION CYANOCOCCUS - II - FERTILITY AND FERTILITY PARAMETERS

Fertility of F-1 hybrids and their open-pollinated progeny was studied for the intersectional cross Vaccinium darrowi Camp x Tr. arboreum Ma rsh as part of a project to determine the feasibility of using V. arbo reum to breed vigorous, drought-tolerant southern highbush blueberry c ultivars. The 16 F-1 hybrids that were studied were vigorous but very low in fertility. Second generation hybrids [MIKs (mother is known) ob tained by open-pollination of the F(1)s] and MIK derivatives were extr emely variable in vigor and fertility, but averaged far higher in fert ility than the F(1)s as evidenced by pollen stainability and amount of pollen produced. F(1)s produced an average of 0.4 seedlings per 100 p ollinated flowers when hand-pollinated in a greenhouse with pollen fro m V. darrowi, 0.2 when pollinated by V. arboreum and 3.4 when pollinat ed by cultivated highbush. Some MIKs that were crossed with other MIKs and with cultivated southern highbush were very high in male and fema le fertility. Female fertility was estimated in greenhouse crosses fro m fruit set, berry weight, number and weight of seeds, number of plump seeds per berry, and number of seedlings obtained. Male fertility was estimated by pollen stainability with acetocarmine and amount of poll en shed, Chromosome counts showed that three F(1)s were diploid and th at four fertile MIKs were tetraploid. One MIK appeared to be aneuploid . Aneuploidy may explain much of the low fertility found in MIK popula tions. These results indicate that good progress is being made in retu rning the hybrid plants to cultivar quality in only a few generations of backcrossing.