Annual variation in fusiform rust infection of slash and loblolly pine seed lots in time-replicated plantings
Trees from two putatively fusiform rust resistant and two susceptible seed lots of slash pine (Pinuselliottii Engelm. var. elliottii) and loblolly pine (P. taeda L.) were planted in 4 or 5 consecutive years at three locations in south Mississippi and examined annually for rust galls that originated the previous year. Disease incidence was usually less than 20% in the first growing season. Resistant and susceptible slash pine had light incidence of rust after about age 5. The susceptible lobloly pine often developed considerable numbers of branch galls after the fifth season, but most were several metres from the main stem of the trees. The resistant loblolly pine of Livingston Parish, Louisiana, never developed more than 23% infection in any 1 year in thirty 80-tree plots. The three remaining seed lots often exceeded 50% infection in some years, but differences among seed lots were usually small. Rankings of the four species seed lots or the six families that made up the resistant slash seed lot varied by trial (year planted and year infected). Replicating experiments in time on high-hazard sites for rust should better define occurrence and importance of location × family interactions.