Biochemical and molecular genetic analysis of flooding tolerance in Echinochloa crus-galli

To compare the regulation of anaerobic metabolism during germination in anoxiatolerant and intolerant plants, enzymes associated with anaerobic metabolism (sucrose synthase, aldolase, enolase, pyruvate decarboxylase [PDC], alcohol dehydrogenase [ADH] and aldehyde dehydrogenase [ALDH]) were assayed in two varieties of Echinochloa crus-galli, formosensis (tolerant) and praticola (intolerant). During anoxia, activities of all enzymes increased 1.5 to 30-fold in both varieties compared to their activities under aerobic conditions. Activities of sucrose synthase, enolase and ADH exhibited the same induction patterns under anoxia in formosensis and praticola. However, activities of aldolase, ALDH and PDC were more strongly induced in formosensis under anoxia (1.2 to 2-fold) than in praticola. These enzymes were also assayed in F₃ families that varied in their anaerobic germinability. For PDC, activities under anoxia in anoxia-tolerant families were similar to those of an anoxia-intolerant family, although the family did not exhibit anaerobic germinability. This suggests that there is no correlation between PDC activity and anaerobic germinability. For ALDH, activities were more strongly induced under anoxia in anoxia-tolerant families than in anoxia-intolerant families, a trend also exhibited by the parents. This indicates that ALDH may play a role in detoxifying acetaldehyde formed through alcoholic fermentation during anaerobic germination.; To analyze quantitative trait loci (QTL) affecting flooding tolerance and other physiological and morphological traits, a restriction fragment length polymorphism (RFLP) map was constructed. One hundred and forty-one loci formed 41 linkage groups. The total map size is 1468 cM and the average size of linkage groups is 35.8 cM. The average distance between markers is 14.7 cM and the range is 0–37.2 cM. Using the linkage map, location and biometrical parameters of QTL were estimated. For flooding tolerance, two QTL were detected and one of them was mapped on linkage group 24. Other traits, including grass morphology, heading date, number of leaves, and plant height were highly correlated. A single QTL for each trait located at very close positions on linkage group 14 and exhibited high phenotypic variance. This suggests that the high correlation between the traits results from QTL with high phenotypic variance at the same or adjacent locations.