The weediness of wild plants: molecular analysis of genes influencing dispersal and persistence of johnsongrass, Sorghum halepense (L.) Pers.

Abstract

Many major weeds rely upon vegetative dispersal by rhizomes and seed dispersal by "shattering" of the mature inflorescence. We report molecular analysis of these traits in a cross between cultivated and wild species of Sorghum that are the probable progenitors of the major weed "johnsongrass." By restriction fragment length polymorphism mapping, variation in the number of rhizomes producing above-ground shoots was associated with three quantitative trait loci (QTLs). Variation in regrowth (ratooning) after overwintering was associated with QTLs accounting for additional rhizomatous growth and with QTLs influencing tillering. Vegetative buds that become rhizomes are similar to those that become tillers-one QTL appears to influence the number of such vegetative buds available, and additional independent genes determine whether individual buds differentiate into tillers or rhizomes. DNA markers described herein facilitate cloning of genes associated with weediness, comparative study of rhizomatousness in other Poaceae, and assessment of gene flow between cultivated and weedy sorghums-a risk that constrains improvement of sorghum through biotechnology. Cloning of "weediness" genes may create opportunities for plant growth regulation, in suppressing propagation ofweeds and enhancing productivity ofmajor forage, turf, and "ratoon" crops.

Evolutionary fate of rhizome-specific genes in a non-rhizomatous Sorghum genotype

“…S. halepense is native to western Asia, but has been introduced and has naturalized in tropical and warm temperate climates worldwide (Holm et al, 1977). Cytological, morphological and molecular genetic data suggest that S. halepense is a naturally formed tetraploid hybrid derivative of Sorghum bicolor, an annual, polytypic African grass species which includes cultivated sorghum; and Sorghum propinquum, a perennial native to moist habitats in southeast Asia (Celarier, 1958;Doggett, 1976;Paterson et al, 1995).…”

“…The Sorghum genus has become a model for dissecting the molecular control of rhizomatousness (Paterson et al, 1995;Hu et al, 2003;Jang et al, 2006). S. halepense L. Pers.…”

Genomic breeding for food, environment and livelihoods

“…Genomic breeding would augment both these methods by helping to directly select useful genetic material in a single generation, a dramatic improvement for long lived species. QTLs that promote plant-microbe interactions and perenniality have, for example, been identified in backcross populations of Sorghum and their progenitor, 'johnsongrass' (Paterson et al 1995;Cox et al 2002).…”

Estimation of Rhizome Composition and Overwintering Ability in Perennial Sorghum spp. Using Near-Infrared Spectroscopy (NIRS)

“…In 2007, there were 614 million acres (248 million ha) of rangeland and pastureland, 36 million acres (15 million ha) of cropland used for pasture, and 37 million acres (15 million ha) of idle cropland in the USA alone [15] that could be utilized in perennial sorghum cropping systems. Improved overwintering ability would be a critical component of perennial sorghum systems and relates directly to the production of rhizomes [16,17], modified underground stems that act as storage and propagation organs [18,19]. Although rhizome depth of growth and derived tiller number have been implicated in overwintering ability [16,20], factors such as rhizome assimilate composition remain poorly characterized.…”

“…Improved overwintering ability would be a critical component of perennial sorghum systems and relates directly to the production of rhizomes [16,17], modified underground stems that act as storage and propagation organs [18,19]. Although rhizome depth of growth and derived tiller number have been implicated in overwintering ability [16,20], factors such as rhizome assimilate composition remain poorly characterized. Furthermore, it is unknown if genetic diversity in sorghum rhizome assimilate composition exists.…”