Importance of temperature in evaluating cotton for resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum race 4

Abstract

AbstractFusarium wilt of cotton (Gossypium spp.) is caused by a soil‐ and seed‐borne fungal pathogen Fusarium oxysporum f. sp. vasinfectum (FOV). Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is a significant threat to cotton production in the United States. The effect of temperature and soil on disease symptoms in cultivars with a range of susceptibility to FOV4 was examined in growth chamber trials. Three upland (G. hirsutum L.) and three pima (G. barbadense L.) cultivars were planted in three types of soils (potting mix and farm soils with and without FOV4 preinfestation) and maintained at four constant temperature regimes (20, 23, 26, and 29 °C). After seedling emergence, each pot was inoculated with conidial suspensions of FOV4 and scored for resistance based on disease incidence (DI), foliar disease severity rating (DSR), and mortality rate (MR) at 7, 14, 21, and 28 d post‐inoculation (dpi). The area under the disease progress curve (AUDPC) based on DSR across the four evaluation dpi was also analyzed. Among the six cultivars tested, Pima PHY 841 RF, Pima S‐6, and the uplands Acala 1517‐08 and FM 2334GLT were the most resistant, whereas upland PHY 725 RF and Pima S‐7 were the most susceptible. The genotypic responses to FOV4 were not significantly (P > .05) affected by differences in temperature regime or soil type. Cotton seedlings manifested more severe symptoms and higher mortality when maintained at 23 °C, followed by 20/26 °C and 29 °C in descending order. The mycelial growth rate was greater at 23/26 °C, whereas plants grew slower at 20/23 °C. There were no differences (P > .05) in DI, DSR, MR, and AUDPC between the inoculated farm soil (with no FOV4 preinfestation) and the inoculated FOV4‐preinfested farm soil, suggesting the unnecessity of using the latter in artificial inoculations. However, the potting soil produced higher (P < .05) DI and DSR at 7 and 14 dpi but lower (P < .05) AUDPC. This growth chamber study demonstrated that 23 °C produced the highest DI, severity, and plant death, providing an important piece of information for screening cotton for FOV4 resistance in breeding and FOV4 disease management in cotton production.