Effect of Planting Date on Spotted Wilt Expression in Differentially Susceptible Peanut (Arachis hypogaea L.) Cultivars.

Peanut spotted wilt caused by Tomato Spotted Wilt Virus (TSWV, Bunyaviridae:Tospovirus) causes significant losses in the SE US. Among the management measures, mid-May plantings are recommended for the region. However, spotted wilt epidemics are highly variable among locations and even from year to year at a single location both in timming and intensity.

Resistant cultivars are the single most important management factor. Nonetheless, genotype x year and genotype x planting date interactions are frequently reported in literature. While consistency in the resistance of cultivars is needed, its genetics remains unknown.

The present study pursued the following objectives: 1) To ascertain the importance of planting dates and location as determining factors of spotted wilt epidemics intensity, 2) To evaluate the consistency in the performance of an array of genotypes with contrasting spotted wilt resistance assessed at different times, and 3) To provide an estimation of how much of the genotypic consistency can be ascribed to genetic causes.

Location was a significant factor determining the spotted wilt ratings among genotypes, while planting date was only significant under light epidemics or just late in the season under heavy epidemics.

The high correlation among assessment dates indicated that the relative performance of genotypes can be perceived early in the season and the genotypic differences tend to persist up until harvest time.

The high values of both Type B genetic correlation coefficients and repeatabilities suggested a strong genetic determination of the observed genotypic differences in spotted wilt intensity ratings. This emphasizes the importance of resistant cultivars in the management of spotted wilt.