Amelioration of Biotic Stress Induced by Onion Yellow Dwarf Potyvirus on Onion Seed Crop Using Nutrition

This study was conducted in the field to evaluate the effect of onion yellow dwarf virus (OYDV) on growth and yield of onion seed crop of two local onion genotypes (var. "Saggai" and Shendi"). It evaluated the possibility of alleviating the disease expression through the use of phosphorus and foliar spray (ADB) fertilizers. OYDV caused pronounced stunting of plants and reduction of leaf length, leaf width, and height and diameter of floral stalk. The virus infection was also associated with significant reduction in yields as demonstrated by umbel size and number of fertile florets carried by the small heads. Nutrition (phosphorus and ADB) was found to have a profound enhancement on growth and seed yield and seed quality of onion plants infected with OYDV. This was demonstrated by a substantial increase in the size of var. "Saggai" leaves (31.0% in length, 17.2% in width) and in the size of "Shendi" floral stalks (28.6% in height, 33.3% in diameter) in response to phosphorus plus foliar spray or phosphorus alone. Significant improvement in yield components, particularly in umbel size and number of fertile florets was obtained from both onion genotypes. The umbel diameter and number of fertile florets decreased in infected plants of cv. "Saggai" by 42.2% and 47.0% and in "Shendi” by 19.1% and 30.6%, respectively. Consequently, the loss in the final seed yield was substantial with reductions of 47.1% and 32.5% in "Saggai" and "Shendi", respectively. Although "Shendi" was comparably affected in its growth parameters to cv."Saggai", but it was affected considerably less in the yield components indicating that "Shendi" is perhaps tolerant to OYDV infection as far as the seed yield is concerned. However, the response to nutrition under test was noticeable for both onion genotypes in all growth and yield components including the final seed yield.