Effect of temperature and daylength on the phenological development of oats (Avena sativa L.)

Abstract

The abiotic factors, temperature and daylength, are mainly responsible for phonological development in cereals. They influence the time of panicle development on the shoot apex, panicle emergence, anthesis and grain-filling which contribute to crop yield and quality. The objective of the research presented in this thesis was to investigate the influence of temperature and daylength on the phenological development of oats. The study was based on two approaches. The first was the traditional photothermal approach which describes the interval between phenological events as influenced by thermal and photothermal time. The second was a more mechanistic approach based on the co-ordinated processes of initiation and expansion of leaves and floral structures on the main shoot apex.

To compare both approaches, phenological events of field grown oat crops, and the number of leaves and floral structures initiated and expanded on the main shoot apex were recorded from three genotypes (Cashel, Drummond and CF435). These were sown (SO) on eight dates (23/04/1996,21/05,06/08,20/09,25/11,22/01/1997, 20/05, and 25/11), at the Crop & Food Research Experiment Station at Lincoln, New Zealand (latitude 43°36'S, altitude 12m). The experiment was a split-plot design with sowing date as the main plot, and genotypes as the subplots, with three replicates. Ten plants per subplot were marked at emergence (EM), and the number of visible leaf tips, the length of the emerged leaf laminae, the emergence of the flag leaf ligule (FL), and anthesis (AN) were recorded. On each sampling date five plants per subplot were removed and dissected under a microscope to record the number of primordia, and the developmental stages of flag leaf primordium (FP), double ridge (DR), and initiation of the terminal spikelet (TS).

Using the traditional photothennal approach, the interval between SO and AN, and intennediate phases (SO-EM, EM-FP, FP-DR, DR-TS, TS-FL, FL-AN), were estimated based on the accumulation of thermal (Tt) and phothermal time (Pt) above a base temperature of 0°C and a base photoperiod of 7h. For each genotype the phases SO-EM (CV between 8 and 10%) and FL-AN (CV between 6 and 15%) were nearly constant in Tt among sowing dates. Using Pt minimized the variation (CV between 6 and 9%) in the interval EM-AN among sowing dates, and also the variation of intermediate phases. It was found that EM could be predicted within an error of 2 days using Tt based on soil temperature (Tt soil) across sowing dates, and that TS and AN could be predicted from EM within an error of 3 days using Pt. Cashel was the fastest developing genotype followed by Drummond and CF435.

The final leaf number (FLN) and phyllochron varied among sowing dates and genotypes. The FLN decreased systematically from April (autumn) to November (late spring) sown crops, and increased again for the January (summer) sown crop. It was highest for CF435 and lowest for Cashel. Also, the FLN was highly correlated with the day length at TS stage which occurred at leaf stage (LS) 4-5 for Cashel, LS 5 for Drummond, and LS 7 for CF435. Thus, equations to predict FLN based on LS required an estimate of phyllochron to determine the daylength at a certain LS.

The phyllochron was not constant in Tt among sowing dates for the same genotype, and it was also shortest for Cashel and longest for CF435. Calculations based on the near apex soil temperature (Tt apex) were less variable than those based on air temperature (Tt air) among sowing dates within a genotype. Indeed, phyllochron based on Tt apex was linearly related to daylength at crop emergence, and could be predicted using this relationship.

Thus, phenological events on the main oat shoot apex could be assessed using the relationships between initiation and development of leaves and floral structures. This is a new framework for oats, and requires information on the relationships between FLN and LS at certain developmental stages, the prediction of FLN, and the prediction of phyllochron. If the FLN and phyllochron are known, than it is possible to predict the stage of FL, and from this point to predict AN, which is then only dependent on Tt accumulation.

In summary, the traditional photothermal approach and the mechanistic approach were used to predict the phenological events of FP, DR, TS, FL, and AN for three oat genotypes. The difference was that the traditional approach used the accumulation of Tt and Pt between developmental events, compared to the more mechanistic approach which used the relationships between visual aspects of the crop (leaf stages) and stages of development on the shoot apex. The effect of temperature (Tt) is accounted for in the mechanistic approach by its effect on the rate of initiation and production of leaves and floral structures on the shoot apex, and the daylength determines the FLN. This is the main conciliation between the traditional and the mechanistic approaches.