The lodging complex in sorghum [Sorghum bicolor(L.) Moench] : morphological, chemical, and anatomical stem features associated with lodging in sorghum

Abstract

Ten sorghum breeding and parental lines, equally divided between lodging resistant (LR) and lodging susceptible (LS) lines, were studied for differences in morphological, chemical, and anatomical features of the stem related to lodging resistance. Plant materials were field-grown at the Texas A&M University Research Center near Lubbock, Texas. Lodging pressure was applied by allowing: 1) soil water deficit to develop during grain-fill in the Water Deficit treatment and 2) No Water Deficit and Water Deficit treatments to remain in the field for an extended period during the winter, subjecting plants to freezing temperatures and strong winds. Water deficit during grain-fill induced lodging (basal) prior to harvest (early November) only in LS lines. Conditions during the overwintering period caused significant lodging (basal and peduncle) of two LR lines and all LS lines in both moisture regimes. Basal stem dry weight per unit length was positively correlated with lodging resistance. Stem chemical analyses showed that LS lines had greater cell wall content in rind and pith tissues which was indicative of the relative inability of these lines to maintain storage supplies of nonstructural carbohydrates in stem tissues. Composition of cell wall material indicated that LR lines had slightly higher lignin content in the rind and pith tissues than LS lines, while cellulose and hemicellulose contents were not consistently related to lodging. Structural failure of stem tissue most frequently occurred in a well defined internodal region -- the intercalary meristem zone. Anatomical differences between LR and LS lines in the intercalary meristem zone contributed more to an of lodging differences than did any of the other measured parameters. Cell wall thickness of hypodermal and vascular bundle sheath cells was generally greater in LR lines than in LS lines, especially in the intercalary meristem zone. In addition to thinner cell walls, histological staining for lignin indicated that secondary cell wall development was lacking in the intercalary meristem zone of LS lines, but appeared normal in LR lines. Rind thickness, hypodermis thickness, and vascular bundle density and size in the intercalary zone, and 10 mm above this zone, generally were not associated with lodging resistance.