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Todd C. Wehner

Cucumber (Cucumis sativus L.) breeders have provided growers with many useful cultivars since production began in the U. S. in the 1600s. The objective of this study was to determine how much breeding progress has been made for yield, earliness, quality, and anthracnose resistance. The experiment was a split-split-split plot in a randomized complete block with 3 replications. Treatments were 2 years (1989, 1990), 2 seasons (spring, summer), 2 production systems (stress, elite), and 14 cultivars (2 important ones from each of 7 time periods, from 1786 to 1982). Plants were grown at Clinton, N. C. using recommended cultural practices, except for the stress treatment, which received half the recommended amount of fertilizer, irrigation, and pesticides. Total yield over 8 harvests increased from approximately 20 Mg/ha for the old cultivars to 30 Mg/ha for the new cultivars. Similar increases were measured for marketable and early yield. Fruit quality (rated 1 to 9) also was improved by breeding, with shape improved 2, and fruit color improved 3 rating points. Part of the improvement in yield was probably due to improved anthracnose resistance. However, improved yield also was obtained in the spring season where anthracnose was absent. In conclusion, the relatively small cucumber breeding effort produced large gains for most traits measured.

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Todd C. Wehner

Several major traits (yield, earliness, quality) of interest to cucumber (Cucumis sativus L.) breeders are quantitatively inherited. The objective of this study was to determine the progress made on such traits using recurrent selection in 4 fresh-market cucumber populations (NCWBS, NCMBS, NCES1, NCBA1). During population improvement, 1 to 2 replications of 200 to 335 half-sib families were evaluated for 5 traits: total, early and marketable fruits per plot, a quality rating, and a simple weighted index (=.2Total/2 + .3Early + .2%Marketable/10 + .3Quality). Families from each population were intercrossed in an isolation block during each summer using remnant seeds of the best 10% selected using the index. Progress was evaluated using a split-plot treatment arrangement in a randomized complete block design with 32 replications in each of 2 seasons (spring and summer). Whole plots were the 4 populations, and subplots were the 11 cycles (cycles 0-9 plus checks). Greatest gains were made for the NCBA1 population, with an average of 45% gain from cycle 0 to 9 over the 5 traits, and for early yield, with an average of 58% gain from cycle 0 to 9 over the 4 populations. Populations were improved for performance in a selected (spring season) as well as a non-selected environment (summer season).

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Todd C. Wehner

Cucumber (Cucumis sativus L.) is one of the more chilling sensitive crops. Chilling resistance could provide growers with protection against late spring frost. Significant differences for chilling resistance were observed among a set of 9 diverse cucumber cultigens when grown at 22 C to 1st true leaf stage, then given a chilling treatment of 4 C for 7 hours in full light (PPFD 500 μmol.m-2.s-1). Two populations, NCWBP and NCES1, were used to measure narrow-sense heritability (estimated as twice the parent-offspring regression coefficient) for chilling resistance. Sets (256/population) of parents and offspring were evaluated in separate tests for seedling resistance. Plants were rated for damage 0 (none) to 9 (dead) on the cotyledons and 1st true leaf, 3 and 5 days after chilling. Ratings were corrected for position in the Phytotron chamber, and log transformations used to normalize the data. Generally, correction reduced the heritability estimates and transformation improved them. Heritability was highest for cotyledon ratings made 5 days after chilling, ranging from 0.35 for NCWBP to 0.70 for NCES1. Ratings of the 1st true leaf were more difficult to make, and produced lower estimates of heritability. Breeders should be able to make good progress in selecting for chilling resistance using this seedling test.