Plant Development and Seed Biology of Windmillgrass (Chloris truncata) in Southern Australia

Abstract

Windmillgrass is a major weed in agricultural systems in northern Australia, and it has now become more common in southern Australia. Because little information is available on the biology of this weed species in southern Australia, studies were conducted to investigate plant development and seed biology. Under irrigated field conditions in South Australia, windmillgrass required 748 to 786 growing degree days from emergence to mature seed production. Freshly harvested seed had low dormancy with 16% to 40% germination. Seeds required light exposure for germination and less than 2% germination was observed in complete darkness. Seed could germinate over a wide temperature range (10 to 40 C) with maximum germination at 20 to 25 C. At 25 to 30 C, 50% germination occurred within 27.3 to 45.5 h, and the predicted base temperature for germination of the two populations investigated ranged from 9.2 to 11.2 C. The sodium chloride concentration and osmotic potential required to inhibit germination by 50% were 51 to 73 mM and −0.27 MPa, respectively. Seedling emergence was completely inhibited by burial of seed, which is consistent with its absolute requirement for light exposure to begin germination. Under field conditions, there was no clear effect of burial depth on seed viability in the first 2 yr with average rainfall, and seeds were completely nonviable after 12 mo. However, in the third year, with low spring–summer rainfall, buried seeds (37% viability after 14 mo) persisted longer than those left on the soil surface (6% viability after 14 mo). This study provides important information on plant development and seed biology of windmillgrass that will contribute to the development of a management program for this weed species in southern Australia.

Glyphosate Resistance of Chloris virgata Weed in Australia and Glyphosate Mobility Are Connected Problems

“…The thermal time to panicle emergence of Chloris virgata is similar to shattercane (Sorghum bicolor) [76]. A related species of Chloris virgata, windmill grass (Chloris truncata) under irrigated field requires 21-23, 43-45, and 74-75 days from seedling emergence to reach tillering, panicle emergence, and mature seed stage [75]. Maximum plant density and biomass in case of windmill grass have been found to be 4.2-28.2 plants m −2 and 8.3-146.1 g dry biomass m −2 depending on location [77].…”

“…Seedling emergence of Chloris virgata was highest (76%) for seeds present on the soil surface and seedling emergence was significantly reduced by burial at 1 (57%), 2 (49%), and 5 cm (9%) soil depth. Furthermore, Chloris virgata seeds buried in the soil persisted longer than those left on the soil surface [75].…”

“…Water stress due to extremely low rainfall over the summer months was the reason for the delayed growth of Chloris virgata under rained conditions when compared to irrigated conditions [75]. Under irrigated conditions, 619 to 730 g of dry biomass m −2 of Chloris virgata (89 days after sowing) was observed; however, this value was much higher than one of its related species, windmill grass (Chloris truncata) (146 g m −2 ) [75].…”

“…In a study related to growth, development, and seed biology of Chloris virgata in South Australia, Chloris virgata seedlings emerging after summer rainfall events under field conditions needed 1200 growing degree days from emergence to mature seed production [65]. Harvested seeds of Chloris virgata were dormant for a period of about 2 months and took 5 months of after-ripening to reach 50% germination [75]. Seedling emergence of Chloris virgata was highest (76%) for seeds present on the soil surface and seedling emergence was significantly reduced by burial at 1 (57%), 2 (49%), and 5 cm (9%) soil depth.…”

“…Chloris virgata has several characteristics like rapid germination and low base temperature (2.1 to 3.0°C) for seed germination enabling it to survive rainfall events in spring, summer, and autumn in South Australia [75]. Minimum tillage due to its benefits like reduced soil erosion and improvement in moisture conservation has resulted in the reduction of soil disturbance in grain cropping fields.…”