Tomato spotted wilt virus (TSWV, Bunyaviridae:Tospovirus) is a major peanut pathogen in the USA. Its management involves, among other factors, the use of resistant cultivars and recommended planting dates.

Ten genotypes with varied degrees of resistance were field tested in two locations and four planting dates with the following objectives: (1) to ascertain the importance of planting dates and location as determining factors of spotted wilt epidemic 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 genotypic consistency can be ascribed to genetic causes. Results indicated that location was a significant factor in determining the spotted wilt damage, while planting date was significant only under a light epidemic or late in the season under a heavy epidemic. The high correlation between assessment dates implied that genotypic performance was perceived early and differences persisted until harvest. High Type B genetic correlation and repeatability suggested a strong genetic determination of resistance.

Heritability is a genetic parameter of paramount importance for efficient plant breeding but no estimates have been published for resistance to TSWV in peanuts. To provide such estimates and assess resistance sources, five populations from three resistant and a susceptible parent were field tested in five environments in Florida, USA. Approximately 36,300 total plants were individually assessed three times for five spotted wilt symptoms using a six level scale. Each environment was individually analyzed using an Animal Model containing block, plot, additive and non-additive terms. High phenotypic (0.80-0.93) and genetic (0.88-0.99) correlation estimates between stunting and spots/mosaic were obtained. Individual-basis heritability estimates showed a wide range (0.01-0.71) although values most frequently were in the low-medium range. This suggests individual selection for resistance to spotted wilt should not be applied in early generations within the tested populations. The resistant parents produced populations with similar breeding values when crossed to the susceptible parent, while the population from a cross between resistant parents exhibited the best breeding values for resistance to spotted wilt.

A published inoculation method was used to study if inoculum age, viral concentration, and extent of rubbing during inoculation affected the frequency of infection. Results showed that neither number of rubbings nor inoculum concentration were important factors. Inoculum showed better infectivity 10 minutes after preparation than at zero or twenty minutes after preparation. Inoculum batch was an important factor; highlighting the fact that viral titer is highly variable even when collected from similar plant tissues. The overall low infection rates suggest that additional work is necessary for mechanical inoculation to be a reliable research tool.