Margy J. Gilpin

ABSTRACT Ascochyta blight of pea ( Pisum sativum L.) is a fungal disease caused by Mycosphaerella pinodes (Berk. & Bloxham) Verstergren, Phoma medicaginis Malbr. & Roum. var. pinodella (L.K. Jones) Boerema, and Ascochyta pisi Lib. that can result in significant reductions to pea yield and quality. To characterize the genetics of resistance and to identify molecular markers for use in plant breeding, quantitative trait loci (QTLs) affecting Ascochyta blight resistance were mapped in F 2:3 and F 2:4 families produced from a cross between resistant breeding line 3148‐A88 and susceptible cultivar Rovar. A linkage map containing 96 loci on 11 linkage groups was constructed for 133 families from this cross. Resistance of progeny lines to natural Ascochyta blight epidemics was examined in field trials at Medina, Western Australia, in 1997, 1998, and 1999. Disease severity was assessed on stems, leaves, and pods by means of separate rating scales. Because pea shows increased susceptibility to Ascochyta blight as it matures, plant reproductive stage was assessed at the time of disease scoring in the 1998 and 1999 trials. Thirteen QTLs were detected for Ascochyta blight resistance on seven linkage groups. Eight of these QTLs were detected in multiple environments or by multiple trait scores. One QTL for plant developmental stage was detected. Linkage of Ascochyta blight resistance QTLs to candidate genes including disease response genes and resistance gene analogs and of the QTL for plant reproductive stage to a pea homolog of the Arabidopsis thaliana CONSTANS gene controlling flowering time in response to photoperiod is discussed.

Abstract A novel starch bread that contained no gluten was found to firm at a rate comparable to a normal standard bread made from wheat flour. Treatment of both the starch and the standard bread with Novamyl, an antistaling enzyme mix, inhibited firming. 13 C CP/MAS NMR studies showed that the decreased firming of the Novamyl‐treated starch bread was correlated with decreased starch retrogradation. For the Novamyl‐treated bread the increase in retrograded starch over six days following baking was about 11% compared to an increase of over 200% for the untreated bread. These results suggests that starch retrogradation is sufficient to cause bread firming.

Hypotheses on the role of gluten in bread staling range from gluten having an anti-firming effect, or no effect on firming, to gluten-starch interactions being essential for bread firming. To test these hypotheses, the firming rate of starch bread made from protein-free synthetic flour was compared with that of starch-gluten breads made from synthetic flours containing 1–15% gluten (Fig. 1). Only loaves of similar specific loaf volume and crumb moisture content were compared to eliminate these parameters as variables that might influence firming rate. The starch breads clearly increased in firmness up to six days, indicating that gluten was not essential to the firming process, starch alone causing bread to firm with time. The starch-10% gluten breads and starch-15% gluten breads had very similar specific loaf volumes, moisture contents and firming rates to that of the starch breads. This indicates that protein possibly has some role in firming, because if only starch has a role in firming then adding gluten would effectively dilute the starch and reduce the rate of firming. We propose that increasing bread firmness results from glucan chains of partially leached amylose and amylo-pectin attached to swollen starch granules forming hydrogen bonds with other starch granules and, to a smaller extent, with gluten fibrils.

As part of our studies on the mechanisms of bread staling, starch bread was used as a research tool that enables us to gain insights into the individual contributions that starch and gluten have on staling. Reconstitution experiments have demonstrated that bread of equivalent specific loaf volume stales at the same rate irrespective of protein concentration, or type of protein. However, other properties of bread, such as specific loaf volume, may be altered by specifically changing the protein component in the flour.