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- Author or Editor: Gregory L. Reighard. x
Pawpaw (Asimina triloba) produces the largest fruit native to the United States. Six linkage groups were identified for A. triloba using the interspecific cross [PPF1-5 (A. triloba) × RET (A. reticulata Shuttlw. ex Chapman)], covering 206 centimorgans (cM). A total of 134 dominant amplification fragment length polymorphism (AFLP) markers (37 polymorphic and 97 monomorphic) were employed for estimating the genetic diversity of eight wild populations and 31 cultivars and advanced selections. For the wild populations, the percentage of polymorphic loci over all populations was 28.1% for dominant markers and Nei's genetic diversity (He) were 0.077 estimated by 134 dominant markers. Genetic diversity and the percentage of polymorphic loci estimated using only polymorphic dominant AFLPs were 0.245 and 79%, respectively, which are comparable with other plant species having the same characteristics. Estimated genetic diversity within populations accounted for 81.3% of the total genetic diversity. For cultivars and advanced selections, genetic diversity estimated by 134 dominant markers was similar to that of wild pawpaw populations (He = 0.071). Thirty-one cultivars and advanced selections were delineated by as few as nine polymorphic AFLP dominant loci. Genetic relationships among wild populations, cultivars and advanced selections were further examined by unweighted pair group method with arithmetic mean (UPGMA) of Nei's unbiased genetic distance. The genetic diversity estimated for wild populations using the clustered polymorphic markers was lower than the result estimated using the nonclustered polymorphic markers. Therefore, this study indicates that the number of sampled genomic regions, instead of the number of markers, plays an important role for the genetic diversity estimates.
Two peach cultivars were budded in 1988 to seedlings from 10 open-pollinated peach and plum lines selected from a 7-year-old peach tree short life (PTSL) field test. Lovell and Nemaguard seedling rootstocks were also budded as controls. The trees were planted in 1989 on a non-fumigated PTSL site near Columbia. South Carolina. Highly significant differences in bloom date, trunk cross-sectional area (TCSA), suckering, bacterial canker infection, and PTSL death were found among the rootstock/scion combinations after four years. Bloom dates when compared to trees on Lovell were advanced by 1-6 days with trees on Blue Goose and BY7446 plums blooming the earliest. Scion TCSA on BY520-8 and BY520-9 peach rootstocks was significantly greater than on Lovell. The plum rootstocks BY7446, Blue Goose, and Edible Sloe had the smallest TCSA. Nemaguard, BY7446, and Edible Sloe had significantly more suckers per tree than Lovell. BY520-9 and Edible Sloe trees had significantly less bacterial canker infection than Lovell. BY520-9, BY7446, and Edible Sloe had the lowest PTSL mortality, and thus hold the most promise as potential rootstocks to replace Lovell on PTSL sites.
We conducted audience surveys at three major peach producer meetings across the United States. We found that the relative importance assigned to fruit quality and tree traits by producers varied across producers’ end markets. Fresh peach producers indicated fruit flavor and size were the most important fruit quality traits, whereas processed peach producers viewed fruit size, fruit firmness, and absence of split pits as being the most important traits for a successful peach cultivar. These results have potential to ensure that peach breeding programs are consonant with fresh and processed peach producers’ needs for fruit and tree traits.