Tomato <i>Mi</i> -gene Resistance-Breaking Populations of <i>Meloidogyne</i> Show Variable Reproduction on Susceptible and Resistant Crop Cultivars

Abstract

Sixteen <i>Meloidogyne</i> isolates from tomato fields in California grown with resistant cultivars were multiplied on resistant tomato in a greenhouse. Of these resistance-breaking isolates, one was identified as <i>M. javanica</i>, and all others as <i>M. incognita.</i> The reproduction of the <i>M. javanica</i> isolate and four <i>M. incognita</i> isolates on six resistant tomato cultivars and on susceptible and resistant cultivars of pepper, sweetpotato, green bean, cotton, and cowpea was evaluated and compared to an avirulent <i>M. incognita</i> population in greenhouse pot trials. On resistant tomato cultivars, there were minor but significant differences between the resistance-breaking <i>Meloidogyne</i> isolates and between the different tomato cultivars. Of the other resistant crop cultivars, pepper was resistant to all isolates and green bean to all <i>M. incognita</i> isolates, while cotton and cowpea allowed reproduction of one of the resistance-breaking <i>M. incognita</i> isolates. The resistant sweetpotato cv. Bonita behaved like resistant tomato, allowing reproduction of all five resistance-breaking isolates but not of the avirulent <i>M. incognita</i>. Our results showed that variability exists among resistance-breaking <i>Meloidogyne</i> isolates, and that isolates overcoming resistance in tomato may also be virulent on resistant sweetpotato.