Seed dry weight response to source–sink manipulations in wheat, maize and soybean: a quantitative reappraisal

A test of the computer simulation model ARCWHEAT1 on wheat crops grown in New Zealand

Knowledge of the changes in physiological traits associated with genetic gains in yield potential is essential to improve understanding of yield-limiting factors and to inform future breeding strategies. Our objective was to identify physiological traits associated with genetic gains in grain yield of winter wheat (Triticum aestivum L.) in the UK. The growth and development of eight representative cultivars introduced from 1972 to 1995 (one tall rht-D1b cultivar and seven Rht-D1b, formerly Rht2, semidwarf cultivars) was examined in field experiments at Sutton Bonington in 1996-1997, 1997-1998, and 1998-1999. A linear genetic gain in grain yield of 0.12 Mg ha(-1) yr(-1) (1.2% yr(-1)) was positively correlated with both harvest index (HI) and aboveground biomass; a quadratic function fitted to the data showed that progress in HI was most apparent during the earlier phase of the 23-yr period, whereas biomass contributed most since about 1983. There was a linear increase across time of 217 grains m(-2) yr(-1), but no change in grain weight. Significant genetic changes across time and correlations with grain yield were also found for preanthesis radiation-use efficiency (RUE, 0.012 g MJ(-1) yr(-1)) and water soluble carbohydrate (WSC) content of stems and leaf sheaths at anthesis (4.6 g m(-2) yr(-1)). Our results suggest that recent genetic gains in grain yield have been based on a combination of improved growth rate in the preanthesis period, which has driven increases in number of grains per square meter, and a larger source for grain filling through increases in stem soluble carbohydrate reserves.

Physiological processes associated with wheat yield progress in the UK

Sirius: a mechanistic model of wheat response to environmental variation

The efficient use of fertilizer nitrogen (N) is crucial to sustainable human nutrition. All crops receive significant amounts of additional N in temperate environments, through fixation or fertilizer use. This paper reviews progress towards the efficient use of fertilizer N by winter wheat (Triticum aesitivum L.) and spring barley (Hordeum vulgare L.) in the UK, acknowledging that on-farm this is governed by economics. Recent multi-site N response experiments on old and modern varieties show that yield improvements since the 1980s have been accompanied by increases in economic optimum N amounts for wheat but not for spring barley. On-farm N use efficiency (NUE) has increased for barley because increased yields with optimum N were associated with compensatory decreases in grain N concentration, whereas on-farm NUE has not increased for wheat because grain N concentration has not changed and improvements in N capture were insufficient to make up for the increased yield. Genetic effects on NUE are shown to differ markedly depending on whether they are determined at a single N rate, as in variety trials, or with optimum N amounts. It is suggested that, in order to elicit faster improvement in NUE on farms, breeding and variety testing should be conducted at some sites with more than one level of applied N, and that grain N%, N harvest index, and perhaps canopy N ratio (kg N ha -1 green area) should be measured more widely. It is also suggested that, instead of using empirical functions, N responses might be analysed more effectively using functions based on explanations of yield determination for which the parameters have some physiological meaning.

Analysing nitrogen responses of cereals to prioritize routes to the improvement of nitrogen use efficiency

The percentage (P) of incident photosynthetically active radiation (PAR) reaching the ground was measured in winter wheat crops throughout the season, and related to projected area index (L) of leaves, plus sheaths and stems when present. Between unfolding of the first leaf and appearance of the flag leaf the mean value for the exponential extinction coefficient (K) was 0·46±0·007. The value did not vary with the growth stage of the wheat and was scarcely affected by experimental treatments, apart from effects resulting from the presence of senescent tissues that intercepted light but whose area was not included in L. After anthesis, in crops having between 340 and 540 ears/m2, between 68 and 89% of incident PAR penetrated to below the ears. Relation between the further penetration to the base of the crop canopy and the area of green plus senescent leaf and stem tissue gave K = 0·50. The relation did not change significantly between anthesis and complete senescence.The relation between P and L was similar whether P was obtained from instantaneous measurements made near midday, 24 h integrals of PAR or percentage ground cover measured photographically.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0021859600079740

I. Pearman

Papers

Estimation of radiation interception by winter wheat from measurements of leaf area