Rate of change in harvest index during grain-filling of wheat

Abstract

SUMMARYA constant rate of change in harvest index (dHI/dt = k) has recently been incorporated into several crop simulation models, so that final grain yield can be calculated from final biomass and the duration of grain growth. Implicit is the assumption that dHI/dt is conservative across treatments and environments. This assumption was tested using data from five experiments grown in the United Kingdom (1973, 1978, 1994) and New Zealand (1992, 1993). The experiments included commercial spring and winter wheat cultivars introduced during the last 100 years and nitrogen, irrigation, sowing date, temperature and CO2 treatments. In all cases, the time course of harvest index (HI) had an initial lag phase, a linear phase and a maturation phase. The linear phase was stable in field-grown crops, except for a reduction in slope after lodging in some crops. Values for dHI/dt, taken as the slope of the linear phase, varied with variety and available nitrogen, were stable for a given variety among years, and were unaffected by water stress. Variation in dHI/dt among varieties was independent of their year of introduction, although those with the Rht2 semi-dwarfing gene generally achieved a higher final HI due to a reduced lag phase. Differences in the duration of the linear phase also caused differences in the final HI after drought. The upper and lower limits of dHI/dt for fieldgrown crops were 1·37 and 0·64% d-1 but, under normal fertility conditions, the variation was between 0·90 and 1·19 % d-1. Results indicated that dHI/dt could provide an effective semi-empirical relationship for predicting grain yield in simulation models. The consistent, linear nature of this relationship suggests a physiological maximum for dHI/dt, for a given species and variety. It may be possible to exploit varietal differences in dHI/dt, and in the lag phase, for yield improvement.

Temperature, CO2 and the growth and development of wheat: Changes in the mean and variability of growing conditions

“…The decreased yields from CE2 were probably caused by the shorter crop growth duration (Table II), resulting in less absorbed PAR in CE2, particularly during grain-fill (Gallagher and Biscoe, 1978;Amir and Sinclair, 1991), and an increase in maintenance respiration rate (McCree and Amthor, 1982). The 10% reduction in grain yield for CE3 may have been caused by the extended lag phase reducing the period of grain-filling (Table II), although no differences in the rate of change of harvest index were detected for this treatment (Moot et al, 1996).…”

“…Secondly, much physiological experimentation is geared to elucidating how differences in growing conditions lead to differences in growth. However, 'What mechanisms lie behind the relatively conservative responses (e.g., leaf number and relative growth rate in this experiment; harvest index, Moot et al, 1996) of plants to wide fluctuations in their growing conditions? '.…”

“…Post-anthesis, ears were hand threshed for measurement of grain dry weights. From these data the beginning and end of grain-filling (maturity) and the rate of change of harvest index during this time, were calculated (Moot et al, 1996). Leaf emergence was monitored twice weekly on the main stems of five randomly selected plants from each cultivar in each treatment.…”

“…There was a high degree of variability within dry matter samples for cv Prince Albert, particularly during the maturation phase (Moot et al, 1996), and this prevented the fitting of logistic curves for this cultivar. For the remaining cultivars, the RGR was estimated to be ca.…”

Simulating Organ Growth in Wheat Based on the Organ–Weight Fraction Concept

“…Other studies have explored the usefulness of timecourse harvest index for predicting grain yield for a given wheat genotype (Moot et al, 1996;Zeng et al, 1996). It is proposed that the near-linear pattern of harvest index increase with time may provide an effective empirical relationship for quantifying dry matter partitioning into grains during the early filling period, although the change patterns exhibit significant differences with genotypes.…”