Nematode quantitative resistance conferred by the pepper genetic background presents additive effects and is stable against different isolates of Meloidogyne incognita

Abstract

Root‐knot nematodes (RKNs), Meloidogyne spp., are a major disease problem in solanaceous crops worldwide, including pepper (Capsicum spp.). Genetic control provides an economically and environmentally sustainable protection alternative to soil fumigants. In pepper, resistance to the main RKN species (M. incognita, M. javanica and M. arenaria) is conferred by the major genes (R genes) Me1, Me3 and N. However, RKNs are able to develop virulence, thus endangering the efficiency of R genes. Quantitative resistance (QR) against Meloidogyne spp. is expected to provide an alternative to R genes, or to be combined with R genes, to increase the resistance efficiency and durability in pepper. In order to explore the ability of QR to protect pepper against RKNs, five pepper inbred lines, differing in their QR level, were tested directly, or after combination with the Me1 and Me3 genes, for their resistance to a panel of M. arenaria, M. javanica and M. incognita isolates. The M. arenaria and M. javanica isolates showed low pathogenicity to pepper, unlike the M. incognita isolates. The QR, controlled by the pepper genetic background, displayed a high resistance level with a broad spectrum of action, protecting pepper against Me3‐virulent as well as avirulent M. incognita isolates. The QR was also expressed when combined with the Me1 and Me3 genes, but presented additive genetic effects so that heterozygous F1 hybrids proved less resistant than homozygous inbred lines. The discovery of this QR is expected to provide promising applications for preserving the efficiency and durability of nematode resistance.

Effectiveness of quantitative resistance conferred by the genetic background of pepper in the control of root‐knot nematodes and influence onto durability of Me1‐ and Me3‐resistant genes in greenhouse conditions

“…One of the specific aims of the present study was to test the effects of quantitative resistance in pepper plants lessen infection by M. incognita in natural infection conditions in the greenhouse where plants are grown. The effects were clear both in genotypes without R‐genes and in those where quantitative resistance combined with the Me3 gene, in agreement with previous observations in controlled conditions (Sánchez‐Solana, Ros, Lacasa et al., ). This confirms the resistance levels identified in “Costal” and “Dátler,” and their effect reducing infection by the nematode when “Costal” was combined with Me3 .…”

“…As regards Me1 , all genotypes carrying this gene showed a high degree of stable resistance to M. incognita, although its effectiveness diminished when introgressed in a very susceptible background (“A1,” with its “Americano” background was more infected than “DH330”). These results corroborate those obtained previously in controlled conditions, both using the same genotypes (Sánchez‐Solana, Ros, Lacasa et al., ), and when Me1 was introgressed in the genetic background of DLL, another variety very susceptible to Meloidogyne spp. (Barbary et al., ).…”

“…However, in the case of Me3 ‐hybrids obtained from “Dátler,” the effect was not statistically significant. This might have been due to the lower quantitative resistance of “Dátler” compared with “Costal,” as well as to the lower expression of resistance in the hybrids due to the additive genetic effects of quantitative resistance (Sánchez‐Solana, Ros, Lacasa et al., ). As regards Me1 , all genotypes carrying this gene showed a high degree of stable resistance to M. incognita, although its effectiveness diminished when introgressed in a very susceptible background (“A1,” with its “Americano” background was more infected than “DH330”).…”

“…Pathogen populations tend to be highly heterogeneous and may show several generations during the same growing season. In previous assessments in greenhouses of the Campo de Cartagena (Murcia, Spain), some varieties of peppers with quantitative resistance showed satisfactory results in the control of M. incognita , using the plants as rootstock (Sánchez‐Solana, Ros, Guerrero et al., ; Sánchez‐Solana, Ros, Lacasa et al., ). However, in these conditions, their effects for preserving the effectiveness of R‐genes are unknown.…”

“…In laboratory conditions, it was seen that this resistance is effective against Me3‐virulent as well as avirulent M. incognita isolates. It has also been found to show additive or partially dominant genetic effects, so the effect of quantitative resistance is expressed when combined with Me1 or Me3 genes, increasing their efficacy in the control of M. incognita (Barbary et al., ; Sánchez‐Solana, Ros, Lacasa et al., ).…”