David W. Davis

Field efficacy of sweet corn hybrids expressing a Bacillus thuringiensis toxin for management of Ostrinia nubilalis (Lepidoptera: Crambidae) and Helicoverpa zea (Lepidoptera: Noctuidae).

Abstract Field studies were done in 1995–1996 to assess the efficacy of three sweet corn hybrids that express the Bacillus thuringiensis (Bt) toxin, Cry1Ab, against two lepidopteran pests, Ostrinia nubilalis (Hübner) and Helicoverpa zea (Boddie). The Bt hybrids tested were developed by Novartis Seeds, using the event BT-11, which expresses Bt toxin in green tissue as well as reproductive tissues including the tassel, silk, and kernel. Bt hybrids were compared with a standard non-Bt control or the non-Bt isoline for each hybrid; none of the hybrids were treated with insecticides during the study. Hybrid efficacy was based on larval control of each pest, as well as plant or ear damage associated with each pest. In both years, control of O. nubilalis larvae in primary ears of all Bt hybrids was 99–100% compared with the appropriate non-Bt check. Plant damage was also significantly reduced in all Bt hybrids. In 1996, control of H. zea in Bt hybrids ranged from 85 to 88% when compared with the appropriate non-Bt control. In 1996, a University of Minnesota experimental non-Bt hybrid (MN2 × MN3) performed as well as the Bt hybrids for control of O. nubilalis. Also, in 1996, two additional University of Minnesota experimental non-Bt hybrids (A684su X MN94 and MN2 × MN3) performed as well as Bt hybrids for percent marketable ears (ears with no damage or larvae). In addition, compared with the non-Bt hybrids, percent marketable ears were significantly higher for all Bt hybrids and in most cases ranged from 98 to 100%. By comparison, percent marketable ears for the non-Bt hybrids averaged 45.5 and 37.4% in 1995 and 1996, respectively. Results from the 2-yr study strongly suggest that Bt sweet corn hybrids will provide high levels of larval control for growers in both fresh and processing markets. Specifically, Bt sweet corn hybrids, in the absence of conventional insecticide use, provided excellent control of O. nubilalis, and very good control of H. zea. However, depending on location of specific production regions, and the associated insect pests of sweet corn in each area, some insecticide applications may still be necessary.

Yield and quality losses caused by common rust (Puccinia sorghi Schw.) in sweet corn (Zea mays) hybrids

Abstract Yield and quality of fresh ears were measured in field plots of selected hybrids of sweet corn (Zea mays L.) that were affected by rust (Puccinia sorghi Schw.) or were nearly rust-free (mancozeb-sprayed). In 1978, 28 hybrids were tested. Losses in total yield ranged from zero in the more resistant entries to nearly 50% in more susceptible entries. In 1979, three cultivars were planted. Yield losses of these cultivars were similar in ranking order to those in 1978, although the loss was greater in late-planted plots because of the greater final severity of the disease. Losses in total yield in late-planted sweet corn were 18%, 26% and 49% for cv. Sugarloaf (most resistant), cv. Jubilee (intermediate) and cv. Style Pak (most susceptible), respectively.

High-temperature-acclimation potential of the common bean: can it be used as a selection criterion for improving crop performance in high-temperature environments?

Abstract The common bean (Phaseolus vulgaris L.) is a heat-sensitive plant species in which excessive abscission of reproductive organs occur during hot weather. This results in ‘split sets’ and yield reductions, and, in extreme heat stress, plant produce few or no pods. We evaluated 74 bean genotypes in terms of leaf heat-tolerance ( ht ) and leaf heat-acclimation potential ( hap ), as expressed by heat killing-time ( hkt ), the time in minutes needed to cause 50% ion leakage from leaf tissue heat stressed at 50°C. Leaf ht is defined as the leaf hkt of plants without prior conditioning at 37°C day/night temperature and leaf hap as the change in leaf ht following exposure of the plant at 37°C day/night for 24 h. Among 74 bean genotypes examined, leaf ht ranged from 5 to 30 min hkt , whereas leaf hap ranged from 35 to 130 min hkt . Positive significant correlations were observed between leaf hap and post-stres performance in plant dry-weight, pod set, pod weight and yield among bean genotypes. However, correlations were not significant between leaf ht and post-stress performance. A relationship between heat resistance—consisting of the combination of ht and hap —and heat injury is proposed. Interpretation of the differential amounts of heat injury among genotypes having different hap , is discussed. We view leaf ht and leaf hap as two distinguishable phenomena. We suggest that, in breeding programs, hap may be the more important of the two, and should be evaluated as a selection criterion for improving crop performance in high-temperature environments.

Ranking of partial resistance to common rust (Puccinia sorghi Schr.) in 30 sweet corn (Zea mays) hybrids

Abstract Thirty sweet corn (Zea mays) hybrids were evaluated for resistance to rust (Puccinia sorghi Schr.) for 3 years in an artificially inoculated field plot at St Paul, Minnesota. On the basis of visual determinations of rust severity, these cultivars were ranked according to level of resistance. All of them allowed at least some rust to develop, but the degree of final rust severity varied considerably. Correlation coefficients between the rust severity scores recorded for the hybrids in all three pairs of years were 0·68 (1978–1979), 0·79 (1978–1980) and 0·86 (1979–1980). Spearmans rank correlation coefficients were 0·76, 0·89 and 0·82, respectively, for the same comparisons.

Mid-parent heterosis and combining ability of European corn borer resistance in maize

Success in breeding maize resistant to the European corn borer has been limited, with the exception of leaf feeding resistance. The inheritance of resistance to leaf, sheath-collar and ear damage in four maize germplasms and their six F1 crosses was evaluated by diallel analysis. Plants in a completely randomized design were artificially infested at the whorl, anthesis or full silk stage of plant development and were evaluated in the field for insect damage. A damage index based on size, number and location of lesions was calculated for each stage. Stowells Evergreen (susceptible) had a mean damage index three to six times that of Maiz Amargo (resistant) at the whorl stage and the progeny plants were more resistant than the susceptible parent. Maiz Amargo and its crosses had significantly lower mean indices than Stowells Evergreen for sheath-collar damage in Year 1 but not Year 2. Zapalote Chico, Maiz Amargo and their cross were significantly less damaged than other genotypes at the full silk stage. Heterosis values indicated an increase in resistance of crosses over the midparent average at all three stages of development. General combining ability (GCA) was highly significant for all types of damage, but specific combining ability was significant only for leaf damage. Based on estimates of GCA, Maiz Amargo was the best source of resistance to leaf and sheath-collar damage and both Zapalote Chico and Maiz Amargo would be good parents for ear damage resistance. Results suggest that resistance at different plant development stages can be combined.

Influence of high temperature on the performance of some Phaseolus species at different developmental stages

SummaryThe effect of short term high temperature exposure on the performance of five Phaseolus species and of long term (continuous) exposure on the performance of P. vulgaris was studied at three growth stages. Phaseolus species subjected to 26.7, 32.2 or 37.3°C for two days showed small differences in the number of pods produced and in visual leaf damage, but large differences in leaf heat killing time, as measured by conductivity. P. coccineus had the shortest heat killing time (20–60 minutes) and P. acutifolius and P. lunatus the longest times (180 and 153 minutes), respectively. The P. vulgaris genotypes were intermediate in killing times to P. acutifolius and P. coccineus. Species response was not consistent with temperature within developmental stage. On average, the number of pods decreased as temperature increased from 32.2 to 37.3°C. Heat killing time and leaf damage also increased with temperature. CO2 exchange rates of plants grown at prolonged high temperatures (30–40°C/20–30°C, day/night) decreased with the age of the plant. Shoot lenght was decreased as high temperature. P. vulgaris genotypes differed on the basis of either short term exposure or of continuous exposure. These results suggest that there may be useful germplasm in Phaseolus for improving heat tolerance.

Inheritance of firmness in raw cucumber (Cucumis sativus L.) fruit

SummaryInheritance of raw cucumber fruit texture (Magness-Taylor Fruit Pressure Tester firmness) was investigated over a 4-year period from 1971–1974. Results from 2 separate but related experiments suggested that firmness was quantitatively inherited with sufficient additive effects to permit gain from selection. In a selection study within 4 F2 populations derived from crosses between ‘firm’ (‘Chipper’ and ‘Gy3’) and ‘soft’ (‘Mincu’ and ‘Green F’) fruit type cultivars, variation among and within F3 and F4 families was significant but overall family means were not significantly higher than the high parent in any of the 4 crosses. Narrow sense heritability estimates for fruit texture were 0.80 in the ‘Mincu’ × ‘Chipper’ population and 0.77 in the ‘Green F’ × ‘Chipper’, ‘Mincu’ × ‘Gy3’, and ‘Gy3’ × ‘Green F’ crosses. In a separate experiment, generation means analysis was used to assess the mode of gene action in 2 crosses: ‘Green F’ × ‘Chipper’, and ‘Gy3’ × ‘Green F’. Additive genetic effects accounted for 98.8% and 99.3% of the total genetic variation within each cross, respectively.

Laboratory bioassays for evaluating sweet corn antibiosis on European corn borer (Lepidoptera: Pyralidae) larval development

European corn borer (Ostrinia nubilalis Hubner) can severely affect commercial sweet corn quality during years of heavy infestation. The isolation and identification of allelochemicals in sweet cor...