Search

Southern California experienced unprecedented megadrought between 2012 and 2018. During this time, Malosma laurina, a chaparral species normally resilient to single‐year intense drought, developed extensive mortality exceeding 60% throughout low‐elevation coastal populations of the Santa Monica Mountains. We assessed the physiological mechanisms by which the advent of megadrought predisposed M. laurina to extensive shoot dieback and whole‐plant death. We found that hydraulic conductance of stem xylem (Ks, native) was reduced seven to 11‐fold in dieback adult and resprout branches, respectively. Staining of stem xylem vessels revealed that dieback plants experienced 68% solid‐blockage, explaining the reduction in water transport. Following Koch's postulates, persistent isolation of a microorganism in stem xylem of dieback plants but not healthy controls indicated that the causative agent of xylem blockage was an opportunistic endophytic fungus, Botryosphaeria dothidea. We inoculated healthy M. laurina saplings with fungal isolates and compared hyphal elongation rates under well‐watered, water‐deficit, and carbon‐deficit treatments. Relative to controls, we found that both water deficit and carbon‐deficit increased hyphal extension rates and the incidence of shoot dieback. Summary statement: We conclude that the ultimate cause of mortality of Malosma laurina in field populations was megadrought and that the proximal cause of mortality was the transition of endemic Botryosphaeria dothidea to an opportunistic pathogen that amplified protracted water stress through physical blockage of xylem water transport. [ABSTRACT FROM AUTHOR]

Neonicotinoid seed treatment (NST) is a routine practice used worldwide to control insect pests in a variety of crops, including maize (Zea mays mays L.). However, previous work indicates that systemic insecticides can compromise plant defenses, counteracting efforts to control insect pests. The goal of this study was to evaluate the effect of thiamethoxam-neonicotinoid seed treatment on the resistance of two maize genotypes (B73 and MC 4050) against the major non-target pest, fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae). In preference and performance assays, we evaluated the effect of NST on fall armyworm behavior and biology. We also determined the influence of NST on induced plant defenses, quantifying phytohormone levels and plant volatile emissions, in treatments with and without fall armyworm herbivory. NST did not affect caterpillar host preference, however it reduced caterpillar performance on the genotype B73 across both maize growth stages (V4 and V6). NST-treated B73 plants also had lower induced volatile production (V4 stage) compared to untreated herbivore-damage plants and lower constitutive salicylic acid (V6 stage). In contrast, MC 4050 was not affected by the insecticide, regardless of growth stage. In conclusion, we found that the effects of NST on maize defenses vary by plant genotype and growth stage, suggesting growers may need to tailor their selection of plant genotypes to avoid negative impacts of NST on plant resistance and ultimately pest control. [ABSTRACT FROM AUTHOR]

Plants can detect herbivore‐induced plant volatiles (HIPVs) from their damaged neighbours and respond by enhancing or priming their defenses against future herbivore attack. Plant communication and defense priming by volatile cues has been well documented, however, the extent to which plants are able to perceive and respond to these cues across different environmental contexts remains poorly understood. We investigated how abiotic changes that modulate stomatal conductance and/or defense signalling affect the ability of maize plants to perceive HIPVs and respond by priming their defenses. During light exposure, when stomata were open and conditions allowed for defense signal biosynthesis, the individual compounds indole and (Z)−3‐hexenyl acetate primed maize defenses. Neither compound primed defenses under environmental conditions that closed stomata and/or altered defense signalling. Moreover, plants were not primed when exposed to indole or (Z)−3‐hexenyl acetate in darkness (while stomata were closed) and then subjected to simulated herbivory in the light, to ensure defense induction. The full blend of HIPVs primed maize defenses in light conditions but suppressed defense induction during dark exposure and wounding. These findings indicate that environmental context is important for plant communication and defense priming and suggest that stomata play a role in plant perception of HIPVs. Summary Statement: This work indicates that environmental conditions impact the ability of Zea mays to detect volatile compounds and prime defense responses, lending support to the idea that plant stomata are involved in volatile uptake and perception. [ABSTRACT FROM AUTHOR]

Chemical cues play important roles in predator–prey interactions. Semiochemicals can aid predator foraging and alert prey organisms to the presence of predators. Previous work suggests that predator traits differentially influence prey behavior, however, empirical data on how prey organisms respond to chemical cues from predator species with different hunting strategies, and how foraging predators react to cues from potential competitors, is lacking. Furthermore, most research in this area has focused on aquatic and aboveground terrestrial systems, while interactions among belowground, soiling-dwelling organisms have received relatively little attention. Here, we assessed how chemical cues from three species of entomopathogenic nematodes (EPNs), each with a different foraging strategy, influenced herbivore (cucumber beetle) and natural enemy (EPN) foraging behavior. We predicted these cues could serve as chemical indicators of increased predation risk, prey availability, or competition. Our findings revealed that foraging cucumber beetle larvae avoided chemical cues from Heterorhabditis bacteriophora (active-foraging cruiser EPNs), but not Steinernema carpocapsae (ambusher EPNs) or Steinernema riobrave (intermediate-foraging EPNs). In contrast, foraging H. bacteriophora EPNs were attracted to cues produced by the two Steinernema species but not conspecific cues. Notably, the three EPN species produced distinct blends of olfactory cues, with only a few semi-conserved compounds across species. These results indicate that a belowground insect herbivore responds differently to chemical cues from different EPN species, with some EPN species avoiding prey detection. Moreover, the active-hunting EPNs were attracted to heterospecific cues, suggesting these cues indicate a greater probability of available prey, rather than strong interspecific competition. [ABSTRACT FROM AUTHOR]

Desiccation-tolerant (DT) organisms can lose nearly all their water without dying. Desiccation tolerance allows organisms to survive in a nearly completely dehydrated, dormant state. At the cellular level, sugars and proteins stabilize cellular components and protect them from oxidative damage. However, there are few studies of the dynamics and drivers of whole-plant recovery in vascular DT plants. In vascular DT plants, whole-plant desiccation recovery (resurrection) depends not only on cellular rehydration, but also on the recovery of organs with unequal access to water. In this study, in situ natural and artificial irrigation experiments revealed the dynamics of desiccation recovery in two DT fern species. Organ-specific irrigation experiments revealed that the entire plant resurrected when water was supplied to roots, but leaf hydration alone (foliar water uptake) was insufficient to rehydrate the stele and roots. In both species, pressure applied to petioles of excised desiccated fronds resurrected distal leaf tissue, while capillarity alone was insufficient to resurrect distal pinnules. Upon rehydration, sucrose levels in the rhizome and stele dropped dramatically as starch levels rose, consistent with the role of accumulated sucrose as a desiccation protectant. These findings provide insight into traits that facilitate desiccation recovery in dryland ferns associated with chaparral vegetation of southern California. [ABSTRACT FROM AUTHOR]