Influence of rainfall, relative humidity, and temperature on the damage caused by the anthracnose-twister of onion

Abstract

Spatiotemporal analysis related to the disease incidence of onion anthracnose-twister caused by Colletotrichum gloeosporioides and Gibberella moniliformis in Sto. Domingo, Nueva Ecija detected an increased magnitude of the disease  in barangays Concepcion, Dolores, San Agustin, San Fabian and San Francisco.The highest disease damage ratings to onions ranged of 3 (moderate damage) to 4 (high damage) on a scale of 1-5, mainly at 10 to 11 weeks after transplantation. The damage distribution revealed high hotspot regions in onion fields in the northern area of San Fabian, the southeasteastern area of Concepcion, and the central east area of Dolores, indicating a clustering of anthracnose-twister incidence. Moreover, Geographic Information System (GIS)-mapped disease damage and weather data discovered that the former had a negligible to weak influence from rainfall with values ranging from 3.57 mm to 3.64 mm, moderate to strong which influenced from relative humidity (RH) (82.86% to 83.03%), and moderate influenced from temperature (22.55 ºC to 22.67 ºC). The regression equation using disease damage and temperature from Dolores, San Agustin, and San Fabian revealed  0.46 to 0.63 damage to decrease whenever the temperature increased. However, the equation contradicted a common theoretical assumptions between RH and disease development stated that increasing RH can promote disease development. Thus, microclimatic RH data from plant canopy or on field conditions can provide more reliable values in regression and correlation analyses as field moisture can be easily altered by farm irrigation.