A Wild Cajanus scarabaeoides (L.), Thouars, IBS 3471, for Improved Insect-Resistance in Cultivated Pigeonpea

Abigail Ngugi-Dawit,Sagadevan G Mundree,Brett Williams,Thomas J.V Higgins,Thi My Linh Hoang

doi:10.3390/agronomy10040517

Abstract

Cajanus scarabaeoides (L.), Thouars, is the closest wild crop relative of cultivated pigeonpea, Cajanus cajan (L.), Millspaugh. This wild pigeonpea has several insect-resistance mechanisms, particularly to Helicoverpa armigera (Hübner). Estimated economic losses in the semi-arid tropics from H. armigera damage in pigeonpea are approximately two billion USD/year. Therefore, it is imperative to improve pest resistance in this crop. In this study, we investigated insect-resistance components in IBS 3471, a C. scarabaeoides accession, and explored the possibility of transferring resistance mechanism/s to cultivated pigeonpea. A detached leaf bioassay revealed that IBS 3471 has more effective antibiosis and antixenosis resistance mechanisms against H. armigera compared to the susceptible C. cajan variety, ICPL 87. To further investigate the antibiosis resistance mechanism, we fed H. armigera larvae a heated and non-heated artificial diet supplemented with lyophilised IBS 3471 leaf powder. Incorporation of IBS 3471 leaf powder inhibited H. armigera larval weight and delayed larval development compared to larvae reared on diet supplemented with ICPL 87 leaf powder. The putative insect-resistance compounds in C. scarabaeoides were heat-labile. Proteomic analysis revealed higher levels of potential insecticidal proteins, namely lectin and cysteine proteinase inhibitor, in wild pigeonpea compared to the cultivated variety. Nutritional analysis and interspecific hybridisation experiments also indicated that IBS 3471 is a potential candidate for improvement of insect-resistance in pigeonpea. This study demonstrates that IBS 3471 has multiple resistance mechanisms against H. armigera, and they are transferable to cultivated pigeonpea.

Highlights

Pigeonpea (Cajanus cajan (L.) Millspaugh) is an important crop that sustains the livelihood of most people in the semi-arid tropics (SAT), where they depend on rain-fed agriculture [1]
All seeds used in this study were obtained from the Australian Grains Genebank (AGG) (Horsham, Victoria, Australia), except for the less susceptible ICPL 20338, the female parent in the interspecific hybridisation, which was obtained from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), (Patancheru, Hyderabad, India)
On the preliminary plant choice bioassay done at the beginning of this study, using leaves, flowers and pods from the different C. scarabaeoides and C. cajan accessions, we observed that the larvae prefer to feed on cultivated pigeonpea and would feed on the wild pigeonpea if they have exhausted the cultivated pigeonpea

Summary

Introduction

Pigeonpea (Cajanus cajan (L.) Millspaugh) is an important crop that sustains the livelihood of most people in the semi-arid tropics (SAT), where they depend on rain-fed agriculture [1]. It is grown worldwide and has an annual production approaching seven million tonnes per year [2]. It is highly drought and salinity tolerant, has a high grain protein content and displays strong resistance against insect pests For these reasons, C. scarabaeoides represents a potential source of resistance to pod borer, pod fly, pod wasp and phytophthora blight in pigeonpea [5]. The role of trichomes in insect defence is established in many plants, including tomato, Arabidopsis and pigeonpea [9,10,11]

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