Variation in resistance of loblolly pine (Pinus taeda L.) and slash pine (P. elliottii Englem.) families against Leptographium and Grosmannia root fungi

Abstract

Leptographium Lagerb. & Melin and Grosmannia Goid. root-inhabiting fungi are the important contributing biotic factors associated with declining loblolly (Pinus taeda L.) and slash pine (P. elliottii Englem.) species in the southeastern United States. The research in this thesis is focused on exploring the variation among the commonly out planted genotypes of loblolly and slash pine by the timber industries in the southeastern United States. Artificial inoculation experiments were conducted on the seedlings and the mature tree roots. Following inoculations, lesion parameters were recorded to access the relative virulence of fungal species and to determine the variation in lesion parameters among the families. Grosmannia and Leptographium species produced dark brown resin filled lesions on the seedling stems and the mature tree roots also exhibited darkened pitch-filled lesions and occlusions around the point of inoculation.

In an effort to study the role of nitrogen and carbon allocation pattern of the genotypes on Grosmannia huntii infection, a greenhouse experiment was conducted. Although, the lesion response indicated successful fungal infection, no significant differences in lesion parameters were noticed between normal and high nitrogen treatment levels. Family differences were noticed in stem total phenolic concentration. Also, the positive correlations between stem total phenolic concentration and family morphological traits (total seedling dry weight, fraction of total dry weight allocated to foliage) for several families show that morphological variables may provide a basis for predicting preformed defense potential. Leptographium terebrantis followed by G. huntii caused larger lesions on seedlings stems and tree roots in the present research. Significant differences in lesion parameters were observed among the seedling families in year 2011 and 2012 experiments. Seedlings inoculation experiments identified some families (L-5, L-20, L-8, and, L-13) that developed consistently smaller lesions, while other families (L-1, L-2, L-3 and L-4) were found to have consistently larger lesions. Variability in lesions was observed between the two fungal species from inoculations on the mature tree roots. However, lesion parameters did not vary significantly among the families. Overall results indicated that ophiostomatoid fungi produced local symptomology and are capable of causing damage to the southern pines. Deployment of these families in the field should take into account the relative risk of other abiotic factors and root-feeding beetles associated with the ophiostomatoid fungi.