Study suggests disease control measures for onion

Onion is considered a fundamental cuisine ingredient. Enjoyed for its unique taste elements that are almost difficult to single out, onions simply add flavor and life to many dishes. This makes onion a universal, highly valued crop that contributes to various economies such as the Philippines.

However, its incredible potential is also met with challenges in terms of production and post-production issues. Data from the Philippine Statistics Authority showed that production of native onion declined 5.1 percent in the fourth quarter of last year, mainly due to adverse climate conditions, lack of planting materials, and disease occurrences.

A group of scientists at Central Luzon State University (CLSU) in Nueva Ecija conducted research on the twister disease, one of the major causes of the decrease in onion production.

Twister disease causes white, oval, sunken spots on the leaves of onion at the early vegetative stage. It also causes twisting and discoloration of the leaves resulting in elongated neck and slender bulbs. It has become prevalent in many onion farms, particularly in the major onion producing provinces of the country which include Ilocos region, Cagayan Valley and Central Luzon.

According to the farmers, frequent rains and high humidity greatly contribute to the proliferation of the disease.

Ilocos, the top producer of native onion at 9.22 thousand metric tons, accounted for 99.8 percent of the national production average.

The project team collected diseased onion specimens from 26 municipalities in eight provinces which included Nueva Ecija, Nueva Vizcaya, Tarlac, Pangasinan, Ilocos Norte, Ilocos Sur, Mindoro Occidental, and Batanes.

From these specimens were isolated the fungal organism. The healthy onion seedlings were then inoculated to induce symptoms. The inoculated seedlings were then studied for disease development with respect to humidity, dew period, light profiles, and temperature.

The inoculated onion seed- lings underwent trials and exposures to various conditions such as 12-24 hour dark dew and photoperiods and 20-350C temperature variations.

The project is still ongoing as it still needs to identify which among the environmental factors can mostly influence the production of the fungal substances, gibberellin and fumonisin, in onion plants. Once final results are generated, the project will then identify the most effective fungicides and of gibberellin inhibitors for the control of the twister disease of onion.

The project received funding support from the Bureau of Agricultural Research (BAR).