Biochemical basis of resistance to pod borer (Helicoverpa armigera) in Australian wild relatives of pigeonpea

Abstract

The domestication of pigeonpea has severely impacted the intrinsic host‐plant resistance (HPR) to pest and diseases, particularly pod borer (Helicoverpa armigera hubner). This study with 41 Australian wild Cajanus genotypes and interspecific hybrids demonstrated a high level of resistance to H. armigera in the accessions of Cajanus acutifolius, C. latisepalus, C. lanceolatus, C. pubescens, and C. reticulatus var. reticulatus. Significant variation in herbivory development and mortality (P < 0.001) was observed in the wild accessions and their hybrids in response to feeding on leaves. A strong positive relationship (R2 = 0.69, P < 0.001) between total phenolic compounds (TPC) and the HPR was observed. Australian wild genotypes demonstrated the role of TPC and the absence of certain flavonoids such as rutin and quercetin in resistant genotypes. The detached leaf bioassay technique separated the wild and domesticated accessions into wild resistant, with herbivory weight difference (HWD) (Day 7–Day 1) ranging between −27 ‐ 104 mg, wild susceptible, with HWD ranging between 124 ‐ 207 mg and domesticated susceptible, with HWD ranging from 208 ‐ 300 mg. Similarly, based on TPC, accessions were also categorised into wild high TPC, with TPC ranging between 32.3 ‐ 42.5 GAE mg/g DW, and wild low TPC had only 17.2–24.8 GAE mg/g DW. Low TPC concentrations were found in domesticated pigeonpea, with 10.7–17.6 GAE mg/g DW. The presence of very high concentrations of the flavone isoorientin, an important antioxidant implicated in the intracellular defence mechanism of cancer therapy, was identified for the first time in wild species of pigeonpea.

Helicoverpa armigera preference and performance on three cultivars of short‐duration pigeonpea (Cajanus cajan): the importance of whole plant assays

“…In our neonate performance experiment, larvae were allowed to select their own feeding site, as opposed the constraints typically placed on them in standard ‘Petri dish assays’ where larvae are confined to feeding on a particular plant part. 36 , 37 , 38 , 39 , 40 Previous studies have shown that first instar H. armigera larvae have a behavioural tendency to move upwards on plants and locate flowers as feeding sites. 41 , 55 , 56 , 57 In our study, after 72 h, regardless of their initial placement location, almost all larvae were found feeding inside flowers, sites devoid of trichomes.…”

“…28,31,32,34,36 Despite the limitations of such approaches, even recent studies persist in screening pigeonpea genotypes with detached-leaf assays. [37][38][39][40] The conditions created in these experiments ignore the behavioural 'choice' of H. armigera larvae, in particular intra-plant movement as larvae tend to move up plants and select floral structures or terminal leaves as feeding sites, [41][42][43] along with detecting and avoiding induced plant defences. 6,44 In this study we evaluated three cultivars of short-duration pigeonpea for resistance against H. armigera (ICPL 87, ICPL 86012, and ICPL 88039) (Table 1).…”

“…Historically, host–plant resistance screening in pigeonpea has relied on small cage oviposition experiments using excised inflorescences 28,33,35 and laboratory bioassays examining larval antibiosis on detached plant parts 28,31,32,34,36 . Despite the limitations of such approaches, even recent studies persist in screening pigeonpea genotypes with detached‐leaf assays 37–40 . The conditions created in these experiments ignore the behavioural ‘choice’ of H. armigera larvae, in particular intra‐plant movement as larvae tend to move up plants and select floral structures or terminal leaves as feeding sites, 41–43 along with detecting and avoiding induced plant defences 6,44 …”

Cajanus platycarpus Flavonoid 3′5′ Hydroxylase_2 (CpF3′5′H_2) Confers Resistance to Helicoverpa armigera by Modulating Total Polyphenols and Flavonoids in Transgenic Tobacco

“…Secondary metabolites involved in plant–herbivore interactions are products of the phenylpropanoid pathway and comprise flavonoids viz., flavanones, flavonols, flavanols, and anthocyanins. Flavonoids are a group of multiuse low molecular weight secondary metabolites that have proven to play vital roles in various plant physiological activities and defence against biotic and abiotic stresses [ 11 , 16 , 17 ]. During the assessment of pod borer resistance response in C. platycarpus, it was observed that there was a structured reprogramming of flavonoid biosynthesis pathway leading to the hyper-accumulation of several flavonoids [ 11 ].…”