Primed to fail: primed acclimation to water stress can lead to greater disease severity and reduced yields in Sclerotium rolfsii -inoculated cultivated peanut ( Arachis hypogaea L.)

BACKGROUND: Primed acclimation is a phenomenon whereby an abiotic stressor early in the vegetative stage of a plant primes defence pathways to the same stressor at later developmental stages. Likewise, cross-stress tolerance is a response whereby an exposure to one abiotic stressor creates a 'stress memory' that can respond more quickly to a later, different abiotic stressor. Cross-priming is a phenomenon whereby an early abiotic stressor confers defence to a late-season biotic stressor. Peanut (Arachis hypogaea L.), an economically important crop in the USA, has exhibited beneficial primed acclimation responses in previous studies. Sclerotium rolfsii, the causal agent of southern blight, can inflict significant economic damage to peanut operations. The purpose of this study was therefore to test for cross-priming against southern blight in two peanut cultivars. METHODS: In this factorial greenhouse study, we instituted four sequential treatments, each with two levels: (1) cv. Florun 331 or cv. Georgia-06G; (2) primary water stress (P-50FC) or primary well-watered (P-100FC); (3) inoculated or control; and (4) secondary water stress (S-0FC) or secondary well-watered (S-100FC), yielding a total of 16 treatments. The primary water stress (PWS) consisted of irrigating plants to 50 % field capacity for 35 days, and the secondary water stress (SWS) was the withholding of any water for 7 days. KEY RESULTS: We documented the absence of a beneficial cross-priming result, in that we did not see reduced southern blight progression among plants exposed to the PWS. Crucially, we observed a three-way interaction between cultivar, PWS and SWS in inoculated plants, whereby the treatment combinations 'Georgia-06G→P-50FC→S-0FC' and 'Florun331→P-50FC→S-100FC' had substantially greater disease severity than their P-100FC counterparts. Serendipitously, we observed reduced secondary transmission of southern blight in P-50FC-treated plants. CONCLUSIONS: Overall, our results caution that drought acclimation might not only fail to deliver crop production benefits but could even have an adverse influence on peanut yields and disease severity.