The Effect of Plant Height on Tan Spot on Durum Wheat in Southern Saskatchewan.
Tan spot [caused by Pyrenophora tritici-repentis (Died.) Drechs.] is the most important leaf disease of durum wheat (Triticum turgidum L. var. durum). Most of the durum cultivars in western Canada are of conventional height but development of shorter cultivars is desirable. Changes in microenvironment resulting from a height reduction might cause greater leaf spot development. The effect of plant height on tan spot of durum wheat was determined in five pairs of genotypes near-isogenic for plant height and five randomly selected populations, each with a semidwarf and a conventional height parent. These were grown in five environments in Saskatchewan (1996-1998 at Swift Current, 1997-1998 at Indian Head), and evaluated for tan spot reaction in a growth chamber. There was no difference in tan spot reaction under controlled conditions between short and tall genotype(s) in each pair or population, although there were differences within each height category. Under field conditions, short genotypes had either equal or greater disease than tall genotypes. Contrasts between all short and tall genotypes also showed that the tall had less disease in 1998 at Indian Head (9.8 for tall, 10.2 for short) and in all years at Swift Current (9.5 and 9.9 in 1996, 8.1 and 8.7 in 1997, 8.5 and 8.9 in 1998, for tall and short, respectively). However, there was genetic variability within populations, with some short having equal or less disease than tall genotypes. Some of these short genotypes also had a low tan spot lesion type under controlled conditions. We conclude that plant height could affect tan spot development in durum wheat under conditions prevalent in southern Saskatchewan, and that this is probably mediated by canopy density.
Climate change impacts on plant canopy architecture: implications for pest and pathogen management
Climate change influences on pests and pathogens are mainly plant-mediated. Rising carbon dioxide and temperature and altered precipitation modifies plant growth and development with concomitant changes in canopy architecture, size, density, microclimate and the quantity of susceptible tissue. The modified host physiology and canopy microclimate at elevated carbon dioxide influences production, dispersal and survival of pathogen inoculum and feeding behaviour of insect pests. Elevated temperature accelerates plant growth and developmental rates to modify canopy architecture and pest and pathogen development. Altered precipitation affects canopy architecture through either drought or flooding stress with corresponding effects on pests and pathogens. But canopy-level interactions are largely ignored in epidemiology models used to project climate change impacts. Nevertheless, models based on rules of plant morphogenesis have been used to explore pest and pathogen dynamics and their trophic interactions under elevated carbon dioxide. The prospect of modifying canopy architecture for pest and disease management has also been raised. We offer a conceptual framework incorporating canopy characteristics in the traditional disease triangle concept to advance understanding of host-pathogen-environment interactions and explore how climate change may influence these interactions. From a review of recent literature we summarize interrelationships between canopy architecture of cultivated crops, pest and pathogen biology and climate change under four areas of research: (a) relationships between canopy architecture, microclimate and host-pathogen interaction; (b) effect of climate change related variables on canopy architecture; (c) development of pests and pathogens in modified canopy under climate change; and (d) pests and pathogen management under climate change.
The chromosomal location of Gai 1 and Rht 1, genes for Gibberellin insensitivity and semi-dwarfism, in a derivative of Norin 10 wheat
SummaryThe gene conferring gibberellin insensitivity, Gai 1, was located on chromosome 4A. This gene is associated with the semi-dwarf habit and consequently it was concluded that Rht 1 is carried by 4A. No recombination was found between Gai 1 and Gai 3, the gibberellin insensitivity gene in “Tom Thumb”-type dwarf wheats, indicating that these genes are either alternative alleles at the same locus or are closely linked.