Screening of onion (Allium cepa L.) varieties for resistance to onion thrips (Thrips tabaci Lindeman) (Thysanoptera: Thripidae) infestation

Onion (Allium cepa) is one of the most important vegetables grown for its nutritional and medicinal values. However, it is highly exposed to onion thrips (Thrips tabaci) which can cause severe yield loss in vulnerable varieties. A study was carried out at the Bindura University Farm Teaching Unit to evaluate the susceptibility/tolerance of ten commonly-grown Zimbabwean onion varieties to thrips infestation. The trial was laid out as a one-factor experiment in a randomized complete block design with 3 replications. Parameters measured for each onion variety were: Thrips population from three to eleven weeks after transplanting, number of lesions, leaf colour, leaf erectness, leaf cross section shape, leaf angle and bulb yield. Onion varieties differed significantly (p < 0.05) with respect to all measured parameters. The varieties Texas Grano, Radium, Australian Brown and Capricio hosted significantly low thrips populations, had low lesion scores and highest bulb yields. The varieties Gauri 91, Malav 21, Red Marvel and White Onion hosted high thrips populations and were also low-yielding. The study recommends the growing of those varieties that support low thrips populations in Zimbabwe as part of integrated management of thrips in onion production. Key words: Bulb yield, host plant resistance, onion thrips, morphological traits.