The influence of induced alterations in morphology and physiology on the tolerance and resistance of plants to pests

The manner and ability of a plant to either compensate for herbivore damage through regrowth or biochemically resist pest attack depends, in part, on the morphology, physiology, and resource allocation pattern of that plant prior to attack. Therefore, environmental factors such as light, nutrients, and moisture can affect the way in which plants respond to pests through inducing alterations in such traits as root/shoot ratio, assimilation rate or allocation to defensive compounds. I experimentally manipulated such resource allocation traits in common bean, Phaseolus vulgaris L., to answer two major questions: (1) How does the induced alteration of resource allocation pattern affect the ability of a plant to grow and to compensate for leaf area removal? (2) How does the induced alteration of resource allocation pattern and physiology affect the ability of a plant to biochemically resist pest attack?;To answer the first question, I exploited the ability of gibberellic acid (GA) to induce enhanced stem elongation and decreased root production in bean to investigate the influence of such an altered resource allocation pattern on plant tolerance to leaf area removal. In both greenhouse and field studies, I found that, in general, plants that had been treated with either a root drench or a foliar application of GA were less able to grow and reproduce following the experimental removal of leaf area than untreated controls. I attribute this to the reduced ability of GA-treated plants to mobilize resources to regrow, produce fruit and fill seeds relative to untreated plants.;To answer the second question, I exposed plants to wind-induced mechanical stress (MS) and analyzed a suite of biochemical defense traits and the biological resistance of MS-treated plants to pests. In general, I found that MS enhanced the activity of such enzymes as peroxidase and cinnamyl alcohol dehydrogenase and enhanced the accumulation of lignin in leaves of bean plants. In turn, leaves of MS-treated bean plants were more resistant to mite reproduction and population growth than leaves from untreated plants. Leaves from MS-treated plants were also more resistant to infection by fungal bean anthracnose than leaves from untreated plants.