Location of Helicoverpa zea (Lepidoptera: Noctuidae) larvae on different plant parts of determinate and indeterminate soybean

Vertical distribution and tissue selection of Helicoverpa zea (Lepidoptera: Noctuidae) adult oviposition and neonates on soybean with an indeterminate or determinate growth habit

Helicoverpa zea (Boddie) is a polyphagous pest that can cause serious damage to crops, including soybeans (Glycine max L.). In soybeans with both determinate and indeterminate growth habits, H. zea larvae are more commonly found on leaves compared to blooms, stems, and pods. Past research demonstrated that H. zea adults tend to oviposit near the upper part of the plant canopy in soybeans with a determinate growth habit. However, ovipositional selection on soybeans with an indeterminate growth habit is unknown. We hypothesized that H. zea would oviposit more uniformly throughout the canopy on indeterminate soybean growth habits due to more diffuse reproductive tissue. We planted field and greenhouse experiments with varieties sharing a similar relative maturity (2 maturity group [MG] 5.2 varieties and 2 MG 5.4/5.5 varieties) but with different growth habits. To test oviposition selection, adult H. zea females were allowed to oviposit under field and caged conditions. We counted the number of H. zea eggs and neonates on each plant tissue type from each of 3 equal parts in the plant canopy: upper, middle, and lower. In both experiments, eggs and neonates were most common on leaves at the top of the plant regardless of soybean growth habit. Consequently, ovipositional selection is likely independent of reproductive tissue availability, and patterns of oviposition through the canopy are similar in growth habits. An improved understanding of H. zea ecology in soybeans relative to indeterminate growth habits may improve recommendations for managing this significant pest of soybean.

Helicoverpa zea (Lepidoptera: Noctuidae) Thresholds and Yield Compensation Between Soybeans with Determinate and Indeterminate Growth Habits

Soybean (Glycine max L.) is an important row crop in the United States and Helicoverpa zea (Boddie) is one of the most serious insect pests in this system. Economic thresholds for H. zea were developed from soybean varieties with determinate growth habits. However, southern USA farmers have recently planted more soybeans varieties with indeterminate growth habits. Trials were conducted with two determinate and two indeterminate varieties within the same relative maturity group. Levels were compared among groups with differing H. zea pressure (low, medium, high, naturally infested) and manipulated using insecticides. Our objectives were to evaluate yield compensation differences among determinate and indeterminate varieties at these different H. zea pressures and to see if the existing economic threshold should be adjusted between growth habits. Since H. zea larval populations varied across trials, we compared trials with low populations, high populations, and no population. Generally, larval counts did not differ among varieties. We found no yield differences among varieties or between growth habits, regardless of H. zea pressure. In the high population tests, yield was highest in the low population plots, but there was no compensation by the plant in yield components except in number of pods with one seed. In contrast, yield components varied widely across varieties, but these differences were independent of H. zea pressure. These results suggest the economic threshold can be used for determinate and indeterminate growth habits, but more research is needed to confirm this with a larger selection of varieties, planting dates, and maturity groups.

Characterization of Mungbean CONSTANS-LIKE Genes and Functional Analysis of CONSTANS-LIKE 2 in the Regulation of Flowering Time in Arabidopsis

CONSTANS-LIKE (COL) genes play important roles in the regulation of plant growth and development, and they have been analyzed in many plant species. However, few studies have examined COL genes in mungbean (Vigna radiata). In this study, we identified and characterized 31 mungbean genes whose proteins contained B-Box domains. Fourteen were designated as VrCOL genes and were distributed on 7 of the 11 mungbean chromosomes. Based on their phylogenetic relationships, VrCOLs were clustered into three groups (I, II, and III), which contained 4, 6, and 4 members, respectively. The gene structures and conserved motifs of the VrCOL genes were analyzed, and two duplicated gene pairs, VrCOL1/VrCOL2 and VrCOL8/VrCOL9, were identified. A total of 82 cis-acting elements were found in the VrCOL promoter regions, and the numbers and types of cis-acting elements in each VrCOL promoter region differed. As a result, the expression patterns of VrCOLs varied in different tissues and throughout the day under long-day and short-day conditions. Among these VrCOL genes, VrCOL2 showed a close phylogenetic relationship with Arabidopsis thaliana CO and displayed daily oscillations in expression under short-day conditions but not long-day conditions. In addition, overexpression of VrCOL2 accelerated flowering in Arabidopsis under short-day conditions by affecting the expression of the flowering time genes AtFT and AtTSF. Our study lays the foundation for further investigation of VrCOL gene functions.