EFFECTS OF HOST-RESISTANCE, TEMPERATURE, LEAF WETNESS, AND LEAF AGE AN INFECTION AND LESION DEVELOPMENT OF PECAN SCAB

The effects of partial host resistance, temperature, leaf wetness dura tion, and leaf age on infection and lesion development of pecan scab w ere evaluated. Trees of cultivars Wichita (susceptible) and Sumner (re sistant) were inoculated with conidia of Cladosporium caryigenum and p laced in mist chambers set at 15, 25, or 35 degrees C. The trees were removed from the chambers after 3, 6, 12, 24, 36, or 48 h of leaf wetn ess and placed in a greenhouse to allow disease development. After 8 t o 16 days, disease began to develop on both 'Wichita' and 'Sumner'. Lo gistic regression analysis showed that the probability of a leaf becom ing infected was greatest for 'Wichita'; it decreased with increasing leaf age and temperature and increased with increasing leaf wetness. L eaves on 'Wichita' were susceptible to infection between 2 and 23 days after budbreak, while leaves on 'Sumner' were susceptible to infectio n from 2 to 18 days after budbreak. Infection frequency, lesion size, and conidia production decreased proportionately with increasing leaf age. The magnitude of this effect was greatest on 'Sumner'. Conidia pr oduction was positively correlated with lesion size, and both were pos itively correlated with infection frequency on both cultivars.