Local Distance of Wheat Spike Infection by Released Clones of Gibberella zeae Disseminated from Infested Corn Residue

Knowledge of the movement of Gibberella zeae (Fusarium graminearum) from a local source of inoculum in infested cereal debris is critical to the management of Fusarium head blight (FHB) of wheat. Previous spatial dissemination and infection studies were unable to completely distinguish the contributions of released inocula from those of background inocula. Clones of G. zeae were released and recaptured in five wheat fields in New York and Virginia in 2007 and 2008. Amplified fragment length polymorphisms were used to track and unambiguously identify the released clones in heterogeneous populations of the fungus recovered from infected wheat spikes collected at 0, 3, 6, and ≥24 m from small-area sources of infested corn residues. The percent recovery of the released clones decreased significantly at fairly short distances from the inoculum sources. Isolates of G. zeae recovered at 0, 3, 6, and ≥24 m from the center of source areas shared 65, 19, 13, and 5% of the genotypes of the released clones, respectively. More importantly, the incidence of spike infection attributable to released clones averaged 15, 2, 1, and <1% at 0, 3, 6, and ≥24 m from source areas, respectively. Spike infection attributable to released clones decreased an average of 90% between 3 and 6 m from area sources of inoculum, and the spike infection potential of inocula dispersed at this range did not differ significantly from background sources. Our data suggest that FHB field experiments including a cereal debris variable should incorporate debris-free borders and interplots of at least 3 m and preferably 6 m to avoid significant interplot interference from spores originating from within-field debris.

Inheritance of Resistance to Two-spotted Spider Mite and Glandular Leaf Trichomes in Wild Tomato Lycopersicon pimpinellifolium (Jusl.) Mill.

Genetics of resistance to Tetranychus urticae Koch and of glandular trichomes of Lycopersicon pimpinellifolium accession TO-937 in a cross between susceptible L. esculentum Mill. `Moneymaker' and resistant TO-937 was studied in a greenhouse experiment. Parents, F1, F2, and two BC1 generations, interspersed with susceptible tomato plants to avoid negative interplot interference, were artificially infested. Mite susceptibility was evaluated by a rating based on plant capacity to support mite reproduction. TO-937, BC1 to TO-937, and F1 were resistant, `Moneymaker' susceptible, and the F2 and the BC1 to `Moneymaker' segregated. Resistance was controlled by a single dominant major locus, but modulated by unknown minor loci. TO-937 presented type IV glandular trichomes, their presence governed by two dominant unlinked loci. Type IV trichome density correlated to resistance; however, a causal relationship between type IV trichomes and mite resistance could not be definitively established. The relatively simple inheritance mode will favor successful introgression of resistance into commercial tomatoes from the close relative L. pimpinellifolium.

Using height to adjust for interplot interference in spring wheat yield trials

Interplot interference can occur in yield trials when genotypes vary for height. We investigated the possibility of adjusting yield for interplot interference by using height measurements in an analysis of covariance. Computer simulation showed that genetic correlation between height and yield would have no impact on analysis of covariance, as well as showing that analysis of covariance would reduce precision in the absence of interference due to height difference. Sixty-five data sets from yield trials conducted in Saskatchewan in 1992, 1993 and 1994 were analyzed to see if analysis of covariance would improve precision of yield estimates. Forty percent of the historical data sets showed evidence of significant interplot interference. In those trials in which interference occurred, yield decreased an average of 0.39% for every centimetre by which the average height of the flanking plots exceeded that of the test plot. Using final height to adjust for interplot interference is effective when genotypes vary for height and when the regression coefficient is significant. Key words: Interplot interference, yield adjustment, height difference, covariate

Assessment of suitable designs for field experiments involving airborne diseases

The suitability was assessed of various designs for field experiments investigating plant diseases caused by airborne pathogens that can be subject to interplot interference. Use of a model to describe such interference showed that the treatments with the most dissimilar effects on controlling the disease should be allocated to experimental plots furthest apart in each block, in order to minimize the interplot interference within a block. When using large square plots, rectangular blocks were more efficient than square blocks in minimizing treatment-comparison biases due to interference between neighbours. For rectangular blocks with the square plots side by side, less biased treatment comparisons were obtained from designs with complete blocks than from designs with incomplete blocks, especially when larger numbers of treatments were included in the experiment. However, when interplot variance is taken into account, incomplete blocks may give better treatment comparisons. Similarly, unbalanced designs composed only of incomplete blocks that yield less biased treatment comparisons may be better than balanced incomplete block designs when interplot variance is low. For high levels of variation, balanced incomplete block designs may be more appropriate, as increasing the precision of the treatment comparisons becomes more important than reducing the bias.

Effect of interference between plots on yield performance in crop variety trials

SUMMARYMethods are described for estimating interplot interference in variety trials. The effects on variety yield performance of interference from varieties in adjacent plots was studied for more than 600 UK National and Recommended List variety trials in the years 1987–1991. The crops examined were barley, wheat, oats, grain peas, beans, oilseed rape, forage maize and sugarbeet. Estimates of differences in variety performance may be biased by as much as 4% in some crops. Factors associated with interference included plant height, standing ability and disease susceptibility. An approach is outlined for limiting the effects of interference through controlled randomization within trials.