Screening techniques and sources of resistance against parasitic weeds in grain legumes

Abstract

A number of parasitic plants have become weeds, posing severe constraints to major crops including grain legumes. Breeding for resistance is acknowledged as the major component of an integrated control strategy. However, resistance against most parasitic weeds is difficult to access, scarce, of complex nature and of low heritability, making breeding for resistance a difficult task. As an exception, resistance against Striga gesnerioides based on a single gene has been identified in cowpea and widely exploited in breeding. In other crops, only moderate to low levels of incomplete resistance of complex inheritance against Orobanche species has been identified. This has made selection more difficult and has slowed down the breeding process, but the quantitative resistance resulting from tedious selection procedures has resulted in the release of cultivars with useful levels of incomplete resistance. Resistance is a multicomponent event, being the result of a battery of escape factors or resistance mechanisms acting at different levels of the infection process. Understanding these will help to detect existing genetic diversity for mechanisms that hamper infection. The combination of different resistance mechanisms into a single cultivar will provide durable resistance in the field. This can be facilitated by the use of in vitro screening methods that allow highly heritable resistance components to be identified, together with adoption of marker-assisted selection techniques.

Release of cowpea line IT99K-494-6 for yield and resistance to the parasitic weed, Alectra vogelii Benth. in Malawi

“…The results are in agreement with other reports which show wide availability in resistant genotypes against A. vogelii (Mainjeni, 1999;Kabambe et al, 2008a, Mbwaga et al, 2000Riches, 1989Riches, , 2001Rubiales et al, 2006;Omoigui, 2012). The results also generally showed that A. vogelii is naturally more prevalent in the mid-altitude sites where all entries are better adapted.…”

“…The witchweed A. vogelii may be controlled through trap crops such as dolichos bean (Lablab purpureus [L.] Sweet) cotton (Gossypium hirsutum L.), okra (Hibiscus esculentus L.), sunflower (Helianthus annuus L.) pea (Pisum sativum L.) and faba bean (Vicia faba L.) (Parker and Riches, 1993). There is generally greater availability of resistant genotypes against A. vogelii (Riches, 2001;Mainjeni, 1999;Rubiales et al, 2006;Omoigui, 2012). Thus, production is threatened by A. vogelii and screening for resistance among existing legumes crops or varieties can help to avoid working with the most susceptible varieties.…”

Response of some chickpea (Cicer arietinum L.) genotypes to Orobanche foetida Poir. parasitism

“…In infested field, several criteria have been used by authors to quantify resistance to orobanche infestation (Rubiales et al, 2006;Abbes et al, 2007a). The best index is the number of orobanche shoots per host plant, which gives the most reliable estimation of the total infestation level (Rubiales et al, 2006).…”

Striga

“…In small millets, early studies towards germplasm characterization and breeding for crop improvement for agronomic traits have not been coupled with the investigation and assessment of the genetic variants for Striga resistance. Hence, characterization of the resistance mechanisms usually follows the identification of resistance sources (Rubiales et al, 2006).…”