Use of grain size distribution parameters to explain variation in small grain screenings of wheat in multi-environment trials involving new cultivars
D. L. Sharma A F , B. J. Shackley B , M. Amjad A , C. M. Zaicou-Kunesch C , M. F. D’Antuono D and W. K. Anderson EA Centre for Cropping Systems, Department of Agriculture and Food, Lot 12 York Rd, Northam, WA 6401, Australia.
B Department of Agriculture and Food, 10 Dore St, Katanning, WA 6317, Australia.
C Department of Agriculture and Food, 20 Gregory St, Geraldton, WA 6530, Australia.
D Department of Agriculture and Food, 3 Baron-Hay Court, South Perth, WA 6151, Australia.
E Department of Agriculture and Food, 444 Albany Highway, Albany, WA 6330, Australia; School of Plant Biology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
F Corresponding author. Email: dsharma@agric.wa.gov.au
Crop and Pasture Science 60(7) 658-666 https://doi.org/10.1071/CP08297
Submitted: 5 September 2008 Accepted: 5 May 2009 Published: 14 July 2009
Abstract
The proportion of small grain screenings is a worldwide problem for wheat growers in water-limited environments and is known to be influenced by both genetic and environmental factors including crop management. This paper follows our previous finding that parameters μ (reflecting point of majority mass of the grain size distribution) and 1/α (reflecting the slope of grain size distribution up to the majority point) of a skew-Laplace distribution can be used to differentiate the tendency of cultivars to produce small grains. The variability of these parameters over environments (15 Cultivar × Time of sowing and 2 Cultivar × Plant population × Nitrogen rates experiments) was investigated in order to indicate their utility in breeding cultivars and managing wheat crops.
The estimated values of both μ and 1/α varied over experiments but the relative cultivar ranking remained similar. Of the genetic and management factors, cultivar had more effect on variance of μ than of 1/α, while applied nitrogen level significantly influenced 1/α. We conclude that: (i) cultivars can be grouped according to their μ and 1/α values; (ii) cultivars owing their lower screenings to high 1/α need a careful optimising of nitrogen inputs, while breeding for high μ is likely to provide stability against small grain screenings; (iii) both the parameters were associated with kernel weight and grains/spike but not grains/m2; and (iv) future research establishing the relationship of 1/α with specific kernel position within the plant will be useful in proposing an ideal ear and plant structure for minimising small grain screenings. When using parameters of the suggested grain size distribution, we suggest the following relevant points be considered: (i) 1/α is not a linear slope, it is related to ‘skewness’; (ii) the peak at majority mass (MM) reflects the tendency to concentrate grain mass and therefore provides an opportunity to increase skewness (1/α) despite a lower μ and a lower mean grain weight; (iii) there is a point up to which skewness of grain size distribution can sufficiently protect against high screenings and is highly dependent upon the value of μ; and (iv) 1/α is a potentially useful parameter nonetheless, because in practice, grain weight may be reduced as number of grains/area is increased in pursuit of high yield through breeding and agronomic practices.
Additional keywords: grain weight distribution, skew-Laplace distribution, rainfed agriculture.
Acknowledgments
Thanks are due to Chapman Valley, Avondale, Merredin, and Esperance Downs Research Support Units for sowing and harvesting field experiments and to Bruce Haig, Melaine Kupsch, and Anne Smith for technical support in the data collection. Additional financial support from farmers through the Grains Research and Development Corporation is gratefully acknowledged.
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