Chestnut blight, caused by the Asian fungus Cryphonectria parasitica, has severely affected chinkapin populations (Castanea pumila), especially those limited to the Ozark mountains (var. ozarkensis). Genetic diversity within and between geographic populations of the Allegheny (var. pumila) and Ozark chinkapin populations was evaluated for development of appropriate conservation strategies. Nuts or dormant buds collected from populations along the range of the species were analyzed using allozymes. A unique allele was detected in populations along the gulf of Mexico. Significant differences in genetic diversity were observed among Allegheny populations, but not among Ozark populations. High levels of genetic identity were detected among widely distributed populations from Florida to Virginia (Allegheny chinkapin populations) and Arkansas (Ozark chinkapin populations).
Fenny Dane and Yuqing Fu
Vincent Njung’e Michael, Yuqing Fu and Geoffrey Meru
Phytophthora crown rot, caused by Phytophthora capsici Leonian, is a devastating disease in commercial squash (Cucurbita pepo L.) production across the United States. Current management practices rely heavily on the use of chemical fungicides, but existence of fungicide-resistant pathogen populations has rendered many chemicals ineffective. Host resistance is the best strategy for managing this disease; however, no commercial cultivars resistant to the pathogen are currently available. Resistance to Phytophthora crown rot in PI 181761 (C. pepo) is an important genetic resource for squash breeders worldwide; however, the underlying genetic basis of resistance in PI 186761 that would allow designing of sound breeding strategies is currently unknown. The goal of the current study was to determine the inheritance of resistance in breeding line #186761-36P, a resistant selection of PI 181761, using phenotypic data from F1, F2, and backcross populations derived from a cross between #181761-36P and a susceptible acorn-type cultivar, Table Queen. The results indicated that resistance in #181761-36P is controlled by three dominant genes (R4, R5, and R6). Introgression of these genes into susceptible cultivar groups of C. pepo will provide an important tool in the integrated management of Phytophthora crown rot.
Njung’e Vincent Michael, Pamela Moon, Yuqing Fu and Geoffrey Meru
Phytophthora capsici Leonian, the causal agent of Phytophthora crown rot in squash (Cucurbita pepo L.), is an economically important pathogen worldwide. Currently, no C. pepo cultivars immune to the pathogen are commercially available, but sources of resistance to Phytophthora crown rot have been identified in a set of 16 C. pepo plant introductions (PIs). Knowledge of the genetic relationships among these accessions and their relatedness to economically important morphotypes of C. pepo would inform breeders’ best strategies for introgressing resistance; however, this information is currently lacking. The goal of the current study was to determine genetic diversity among the resistant accessions and their genetic relatedness to susceptible morphotypes of subspecies pepo (Zucchini and Pumpkin) and texana (Acorn, Straightneck, and Crookneck) using 39 SSR markers. The markers revealed 132 alleles averaging 4.40 alleles per locus and had a mean polymorphic information content (PIC) and gene diversity of 0.44 and 0.49, respectively. CMTp235 had the highest PIC and gene diversity of 0.80 and 0.82, respectively. Hierarchical clustering by UPGMA and principal coordinate analysis (PCOA) revealed grouping into two major C. pepo subspecies, texana and pepo, with all the resistant accessions grouping in the latter. In order of increasing genetic distance (GD), the resistant accessions were least distant to Zucchini (GD = 0.34), followed by Pumpkin (GD = 0.40), Crookneck (GD = 0.56), Acorn (GD = 0.60), and Straightneck (GD = 0.61) morphotypes. Mean GD among the resistant accessions was 0.31 and was highest between PIs 615142 and 615132 (0.61). Based on genetic similarity, PIs 174185 and 181761 (disease severity ≤1.4) would be the best sources of resistance for transfer into subspecies texana and pepo, respectively. Overall, the results presented here support a closer genetic relationship between the resistant accessions and morphotypes of subspecies pepo than those of subspecies texana.
Alan Chambers, Pamela Moon, Yuqing Fu, Juliette Choiseul, Jinhe Bai, Anne Plotto and Elizabeth Baldwin
Fragaria vesca is a diploid strawberry species that produces gourmet, aromatic fruits with only limited commercial production because of its relative obscurity. Most F. vesca research focuses on genetics and fruit aroma, but yield and fruit quality data across diploid accessions are lacking. Sixteen F. vesca accessions were grown in replicated field plots in southern Florida to measure field performance and fruit quality over multiple harvests during a single growing season. Accessions ‘Reine des Vallees’, ‘Baron Solemacher’, ‘Fragolina di Bosco’, and ‘Reugen’ all had significantly higher yield (115–140 g/plot/week) and fruit number (117–139 fruit/plot/week) compared with ‘Bowlenzauber’, ‘Attila’, ‘Ali Baba’, and ‘Pineapple Crush’ (31–57 g/plot/week and 32–60 fruit/plot/week) during peak production. Total average yield ranged from 240 g (‘Pineapple Crush’) to 1194 g (‘Baron Solemacher’) per plot of 10 plants. Fruit number and fruit yield were highly correlated (R 2 = 0.96) for all accessions, and there was no significant difference in fruit weight among accessions through the entire season. Total soluble solids ranged from 10.9 to 13.5 °Brix, and fructose, glucose, sucrose, and total sugars ranged from 15.3 to 22.1, 13.5 to 20.0, 0.1 to 2.7, and 29.7 to 42.5 mg/g, respectively, fresh weight. Acidity ranged from 1.00% to 1.18% citric acid and was not consistently significantly different among accessions over multiple harvests. Forty-two aroma compounds were putatively identified over three harvests for each accession and included mostly esters and ketones with a few alcohols, terpenes, and aldehydes. The majority of these compounds were similarly abundant over harvests and among accessions with a few exceptions, including methyl anthranilate. These results are the first in-depth study of yield and fruit quality for a large number of F. vesca accessions that could lead to increased cultivation of this species for local markets.