Monitoring virulence in Asian rice gall midge populations in India

Abstract

The Asian rice gall midge, Orseolia oryzae (Wood‐Mason) (Diptera: Cecidomyiidae), is a major pest of rice [Oryza sativa L. (Poaceae)] in India. Breeding resistant varieties and their cultivation has been the main approach to manage this pest. However, the breakdown of resistance conferred by the major genes, deployed one at a time, through evolution of virulent biotypes has become a major setback to this approach. Development of polymerase chain reaction‐based molecular markers for eight of the 10 resistance genes and their possible use in marker‐assisted selection has enabled breeders to pyramid resistance genes for achieving durable resistance. However, the choice of resistance genes needs to be made with a better understanding of the virulence composition of the pest populations in the target area and the genetics of plant resistance and insect virulence, as the rice–gall midge interaction is a gene‐for‐gene one. We adopted a single‐female test and coupled it with a modified F2 screen test to note the virulence composition of gall midge populations and estimated the frequency of virulence alleles for adaptation at three pest endemic locations in India, namely, Warangal, Ragolu, and Raipur. Results on biotype composition showed heterogeneous pest populations in all the tests and at all the locations. Tests at Warangal repeated after 8 years showed a rapid increase in frequency of the virulence allele conferring adaptation to the plant resistance gene Gm2 as compared to that of the allele for adaptation to the resistance gene Gm1. This is probably the first direct measurement of a durability parameter of plant genes conferring insect resistance. Results supported earlier observations that sex‐linked virulence against Gm2 makes it less durable. The sex ratio did not deviate from the expected 1:1 ratio at Warangal, but at Ragolu females outnumbered males.

A novel mechanism of gall midge resistance in the rice variety Kavya revealed by microarray analysis

“…Most of but not all, R-gene-triggered resistance is accompanied with HR. Insect resistance with HR-like symptoms have also been observed in cases such as wheat (Triticum aestivum) Grover 1995), peach (Prunus persica) resistance to the aphid Myzus persicae (Sauge et al 1998), rice (O. sativa) against the gall midge O. oryzae (Bentur et al 2003), willow (Salix viminalis) tree varieties against the gall midge (Dasineura marginemtorquens; Hoglund et al 2005) and bean (Phaseolus vulgaris) resistance to the bean-pod weevil (Apion godmani; Garza et al 2001). Cell death that occurs during HR+ type resistance is reported to be controlled by the oxidative burst (Atkinson et al 1996;Heath 2000), production of NO (Delledonne et al 2002), and the interaction between some of these different signaling pathways (Delledonne et al 2002).…”

“…This could also be a case of "extreme resistance mechanism" which is devoid of cell death. It is also noteworthy that resistance conferred by Gm1 gene in the rice variety Kavya is more durable than that conferred by other gall midge-resistant genes which exhibit inducible HR+ type resistance (Bentur et al 2008). Nevertheless, this novel mechanism of resistance needs further characterization.…”

“…Eleven resistance (R) genes (designated Gm1 through Gm11) have been identified, so far, from different rice varieties (Himabindu et al 2010). Seven distinct gall midge biotypes, differing in their virulence against these R genes have been reported (Bentur et al 2003;Vijaya Lakshmi et al 2006). The interaction between the plant-insect is on gene-for-gene basis and defense response is triggered by initial feeding of the maggot within 48 h. Two distinct interactions are noted when gall midge attempts to feed on a rice plant.…”

“…This insect is essentially a wetseason pest and can cause severe damage under favorable weather with high humidity and moderate temperatures, resulting in an estimated annual yield loss amounting US$ 80 million in India (Bentur et al 2003) or about US$ 500 million in Asia (Herdt 1991). The genetics of rice gall midge interaction is well-characterized.…”

Rice–gall midge interactions: Battle for survival

“…Also, studies on inheritance of virulence in biotypes suggested a single recessive gene conferring virulence (Bentur et al 1992). Some of the virulence genes are sex-linked (Behura et al 2000, Bentur et al 2008. Thus a genefor-gene relation was evident between rice R genes and gall midge biotypes (Nair et al 2011), as evident between the Hessian fly biotypes and wheat R genes (Harris et al 2003).…”