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- Author or Editor: Gregory L. Reighard x
- Journal of the American Society for Horticultural Science x
Peach [Prunus persica (L.) Batsch (Peach Group)] trees bloom in response to chilling and postrest heat accumulation. The peach cultivar Coronet exposed to a graft-transmissible, infectious agent known as peach latent mosaic viroid (PLMVd) blooms at a different time than noninoculated trees of the same cultivar. To determine if chilling requirements differed between trees inoculated with PLMVd and noninoculated controls, fruiting shoots collected from the orchard and artificially chilled containerized trees were forced in a greenhouse. Additional artificially chilled containerized trees were forced under constant temperatures in growth chambers to determine if postrest heat accumulation requirements differed. There was no difference in the chilling requirement of the fruiting shoots collected from the field although the shoots exposed to PLMVd had a delayed response and fewer responded to greenhouse forcing conditions. The containerized trees also showed no differences in chilling requirements during winter 1999 or 2000. Trees inoculated with PLMVd had a significant delay in bloom. Growth chamber data revealed a significantly higher base temperature for heat accumulation in the PLMVd inoculated trees.
Peach [Prunus persica (L.) Batsch (Peach Group)] trees infected with peach latent mosaic viroid (PLMVd) have been associated with phenological changes including delay in bloom, reduced shoot vigor, and early autumn defoliation. In order to further characterize the changes occurring in trees inoculated with PLMVd, total fatty acid content was measured for floral buds during release from dormancy in `Coronet' peach trees. Palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2), and linolenic (18:3) acids were the major fatty acids in dormant and releasing peach buds of both control and PLMVd-inoculated (VI) trees. The degree of unsaturation increased immediately following release from dormancy in both the control and VI trees. However, desaturation of linoleic acid to linolenic acid was significantly inhibited in VI trees, which was accompanied by a concomitant delay in the resumption of growth. The disparity between the control and VI trees in the progression of increased fatty acid unsaturation continued through petal fall. The presence of PLMVd in `Coronet' peach trees slowed membrane fatty acid desaturation during release from dormancy and suggested that metabolic pathways involving fatty acid desaturation were linked to the delayed phenology of the VI trees.
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.