MODIFIED EXPRESSION OF THE N-GENE FOR SOUTHERN ROOT-KNOT NEMATODE RESISTANCE IN PEPPER AT HIGH SOIL TEMPERATURES

Heat stability of the N gene that confers resistance to the southern r oot-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood in pepper (Capsicum annuum L.), was determined at 24, 28, and 32 degrees C. Responses of resistant hell pepper cultivars Charleston Belie and C arolina Wonder (homozygous for the N gene) and their respective suscep tible recurrent backcross parents, 'Keystone Resistant Giant' and 'Yol o Wonder B', to M. incognita were compared. Numbers of eggs/g fresh ro ot, reproductive factor of M. incognita, numbers of second-stage juven iles in soil, egg mass production, and root galling increased (P < 0.0 5) for all cultivars as temperature increased. The response of the res istant cultivars to temperature increase was less dramatic than the re sponse of the susceptible cultivars, Both 'Charleston Belle' and 'Caro lina Wonder' exhibited a partial loss of resistance at 28 and 32 degre es C. Reproduction of M. incognita was minimal on the resistant cultiv ars at 24 degrees C, but increased at higher temperatures. However, at 32 degrees C reproduction of M. incognita on the resistant cultivars was only 20% of that on the susceptible cultivars and root gall indice s were within the range considered moderately resistant. Unlike the su sceptible cultivars, the shoot dry weights of the resistant cultivars were not suppressed at 32 degrees C. This suggests that ''Charleston B elle' and 'Carolina Wonder' may be somewhat tolerant to M, incognita a t high soil temperatures. Although results indicate a partial loss of resistance occurred in 'Charleston Belle) and (Carolina Wonder' under high soil temperatures, resistant cultivars may be a useful component of cropping systems designed to manage M. incognita in hot climates.