Physiological control of Hagberg falling number and sprouting in winter wheat and development of a prediction scheme

Abstract

The aim of this research was to understand the causes of low Hagberg falling number in the UK and formulate a prediction scheme. Literature review revealed three recognised routes of alpha-amylase production, causing low HFN, with the possibility of a fourth. Visits to researchers operating differing types of HFN prediction schemes in Finland and France allowed identification of the components of those schemes appropriate for use in the UK. Factors influencing the four routes of alpha-amylase synthesis in the UK were therefore investigated in multi-site field, controlled environment and laboratory studies.

Lowering of HFN by pericarp amylase (a-AMY-2) isozyme activity, was demonstrated by reconstitution of flours with immature grains. This highlighted the possibility of retention of pericarp alpha-amylase activity (RPAA) as a route to low HFN in the UK. Experiments with air-drying and desiccant spraying indicated these as possible control measures for RPAA.

A comparison of crops at two sites in two years did not show a relationship between pre-maturity alpha-amylase accumulation in the absence of sprouting (PMAA) and grain drying rate, reported by other workers. Transfers of developing wheat plants between warm and cool controlled environment cabinets during grain development showed induction of PMAA by both cold and heat shock, even in cultivars such as Pastiche which have never shown PMAA in the field. The factors inducing PMAA were too complex to allow modelling with meteorological data.

Pre-maturity sprouting (PrMS) during the grain dough stage was demonstrated, by isolated grain germination and grain cutting experiments, to be caused by severe cold, wet weather, by pericarp damage, or interaction of the two factors. Increased susceptibility to PrMS was found to be associated with infestation of wheat grain by the orange wheat blossom midge (Sitodiplosis mosellana) during grain development. Midge-damaged grains showed only the characteristic pattern of plant germination amylases, with PrMS enhanced by splitting of the pericarp caused by larval feeding, leading to dormancy break and germination.

Multi-site field studies at four sites over four years were used for the investigation of the relationship between dormancy and temperature with the aim of predicting post-maturity sprouting (PoMS). The relationship found between dormancy index of harvested grain and temperature in France was not seen with UK data. A relationship was found between dormancy duration and temperature accumulated during grain development, for sprouting resistant cultivars, although it was too weak to allow modelling of dormancy.

Consideration of the visits abroad and the progress in defining the complex routes of alpha-amylase synthesis in the UK allowed development of a prototype scheme for HFN forecasting. During the field studies, a good relationship between pre-harvest HFN and combine harvest HFN, in the absence of subsequent rain, was found. Therefore, combine harvest HFN potential can be assessed at about 35% grain moisture (Stage 1). Crops with low HFN due to PMAA, PrMS or RPAA can be given low harvest priority. Improvement of crops with RPAA may be possible, but not of crops with PMAA or PrMS. Assessment of the level of dormancy (or germinability) in crops in Stage 2 (using the sample as Stage 1) with a germination test allows identification of crops with a high HFN potential but at high risk of HFN loss (due to PoMS) in poor weather. These crops would benefit from an early, high moisture harvest. Trial operation of the scheme in 1996 and 1997 allowed assessment of the logistics of operating such a scheme and allowed predictions of combine harvest HFN to be made with a success rate of 75-85%.