VIEW ARTICLE

Resistance

Influence of Needle Age and Inoculum Spore Density on Susceptibility of Longleaf Pine to Scirrhia acicola. A. G. Kais, Principal Plant Pathologist, Southern Forest Experiment Station, Forest Service, U. S. Department of Agriculture, Gulfport, Mississippi 39501; Phytopathology 67:686-688. Accepted for publication 16 November 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-686.

Susceptibility of fascicled needles to infection by Scirrhia acicola decreased as needles elongated and matured. Almost all needles of young seedlings inoculated at age 8 wk were severely infected within 4 wk of inoculation. For more mature seedlings (12 wk of age or older when inoculated), moderate infection occurred within 8-12 wk. Young plants with newly expanding needles were so susceptible that even light inoculations produced rapid, massive tissue mortality. In contrast, needles of seedlings inoculated at 14 wk of age were moderately resistant to both light and heavy inoculations. For mature seedlings, the needle tissue proximal to the stem was more susceptible to infection than either medial or distal tissue of the same needles.