Environmental Factors Affecting Pre-Maturity <i>Alpha</i>-Amylase Activity in Winter Wheat (<i>Triticum aestivum</i>)

Pre-maturity <i>alpha</i>-amylase activity (PMAA) in the absence of sprouting is one of four causes of low Hagberg falling number (HFN) in UK winter wheat (<i>Triticum aestivum</i>), reducing the quality and value of milled flour. Other causes include the retention of pericarp <i>alpha</i>-amylase activity (RPAA), pre-maturity sprouting (PrMS) and post-maturity sprouting (PoMS). This thesis investigated the effects of environmental factors on PMAA which currently occurs in a variable and unpredictable fashion under UK weather conditions.<br></br><br></br>A multi-site field experiment on four cultivars (Haven, Hornet, Pastiche and Riband), at four sites (Harper Adams University College, University of Nottingham, University of Aberdeen and ADAS-Bridgets) between 1994-1996 was undertaken to:- establish the frequency of the causes of low HFN; examine the relationship between grain drying-rate and PMAA; determine if it was possible to predict combine harvest HFN.<br></br><br></br>A range of techniques including a visual sprouting assessment, fluorescein dibutyrate staining, iso-electric focusing and a beta-limit dextrin gel and iodine staining test were used to allow the cause of low HFN to be established. Of the forty crops analysed, 22 cases (45%) had detectable amounts of <i>alpha</i>-amylase activity. PMAA was identified solely in 2 cases (5%), in combination with PoMS in 8 cases (20%), in combination with RPAA in one case (2%), with PoMS occurring solely in 11 cases (28%). The HFN fell below the breadmaking standard of 250 s in 18 of the 36 site x year x cultivar combinations analysed. This was attributed solely to PMAA in two cases (11%), a combination of PMAA and PoMS in a further eight cases (44%) and solely to PoMS in eight cases(44%). There were no cases where PrMS or RPAA reduced the HFN to below 250 s.<br></br><br></br>The hypothesis that PMAA is related to the grain drying-rate between 40-20 % moisture content was tested. Grain drying-rate was determined by linear regression analysis using moisture content measurements made at regular intervals during grain development. In site x year x cultivar combinations where PMAA was detected the grain drying-rate was significantly (P = 0.047) lower (mean = 1.90 <i>cf</i>. 2.30% moisture loss day^-1), suggesting a slow grain drying-rate enhances PMAA. However, the low frequency of occurrence of PMAA in isolation prevented quantification of this relationship.<br></br><br></br>Initiation of PMAA in the grain, was shown to occur from a grain moisture content of 47.8%. A pre-harvest sample taken by hand at 850 °C-days (35 % moisture, Zadoks growth stage 85-87) was shown to enable a prediction of combine harvest HFN to be made in the absence of subsequent rainfall and PoMS. The 95 % confidence limits associated with this HFN prediction were however wide.<br></br><br></br>The hypothesis that transient changes in temperature early in grain development may affect PMAA, before the onset of any grain drying-rate effects, was tested in five controlled-environment cabinet experiments. Of 36 cultivar x time of transfer combinations undertaken from a 16/ 10°C to a 26 /20°C temperature regime, six led to a significant increase (P < 0.05) arid one led to a significant decrease in PMAA. Of the 18 cultivar x time of transfer combinations undertaken from a 25 / 20°C to a 16 / 10°C temperature regime, one led to a significant increase and one led to a significant decrease in PMAA. A comparison between the field and controlled-environment experiment results highlighted that after conditions putatively stimulating PMAA had been encountered, subsequent environmental factors, such as mean temperature and relative humidity may also affect PMAA.<br></br><br></br>It was concluded that PMAA can be enhanced by transient increases in temperature before the grain reaches 40% moisture content and by a slow grain drying-rate between 40-20% moisture content. The variability in the results, however, also suggested other environmental factors were influencing PMAA.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

The Open University

Year dc:date.issued

1999

Author dc:creator

• Major, Bernard James

Language dc:language

en