Evaluation of Resistance of Selected Green Gram (Vigna Radiata) Varieties Against Insect Pests Infestation During Long Rains Season, Tharaka North and South Sub-Counties, Kenya
Abstract
Green grams farming plays a vital role in Tharaka Nithi County and the country at large by ensuring food security, creating employment for rural households and greatly contributing to the national economy. However, the infestation of insect pests on the green grams has drastically affected its production in the country and therefore the current study seeks to identify the green gram variety that can resist insect pests for better productivity. This study was conducted in Mukothima and Gatunga wards in Tharaka North and Tharaka South Sub-counties during one growing season between March-May, 2023, the period of long rains. The study presents insect pests attacking greens in the field, the most resistant green gram variety among the selected varieties and the relationship between insect pest infestation and overall yields. Sticky insect traps were set to capture pests, manual counting of pests and a dissecting microscope were used to count minute insect pests. Levels of leaves and pod damages were also checked and the resulting yield was weighed using a weighing balance. Whiteflies and aphids were the major pests in the green grams with African pod borers and leaf weevils causing insignificant levels of damage (Whiteflies-Uncle-334.3, Biashara-446.33, Karembo-352.8, Tosha- 420, Nylon- 515.7; Aphids- Uncle-323.9, Biashara-459.6, Karembo-394.5, Tosha- 413.6, Nylon- 468.8). The levels of damage on leaves and pods recorded were as follows; Nylon (severity of leaves damage-1991.0, incidence of pods damage- 0.328, number of holes poked in leaves- 3.11) proved to be the most resistant to whiteflies and aphids and Ndengu Tosha (severity of leaves damage-2564.76, incidence of pods damage-0.599, number of holes poked in leaves-4.45) the least
resistant to whiteflies and aphids. The relationship between insect pest infestation and yields showed that an increase in the number of insect pests led to a decrease in yields. Some varieties’ yields were affected by whiteflies, others by aphids and others by both (Karembo-aphids (0.3935), Uncle- aphids (0.525), Biashara- whiteflies (0.2033), Nylon- none, Tosha- whiteflies (0.407) and aphids (0.297)). All the means of the
analyzed data were separated using Tukey’s HSD (Tukey’s Honestly Significant Difference Test) at 5% significance. In conclusion, insect pests (whiteflies and aphids) cause significant levels of losses in green gram which differ in different varieties (Nylon having the least yield loss and Tosha having the highest loss in yield). There is a need to breed varieties that are resistant to whiteflies and aphids. The results of the study are useful in variety selection during planting to minimize losses caused by insect pests and
advise KALRO on the best variety.