Search

The competitive abilities of a wide range of genotypes of wheat (Triticum aestivum L.) and durum wheat (Triticum durum Desf.) against Lolium rigidum Gaud. (annual ryegrass) were examined to determine the potential for breeders to select strongly competitive varieties. Considerable potential within the wheat genome to breed varieties with greater competitive ability was demonstrated. In 1993, 250 genotypes from around the world were screened and in 1994 a subset of 45 (mainly Australian) genotypes were further examined. A uniform density of L. rigidum reduced grain yield of wheat by up to about 80% in 1993 and to 50% in 1994, depending on wheat genotype. Reduction in grain yield was correlated with L. rigidum dry matter. Wheats varied in competitive ability with source, and durum wheats were less competitive than T. aestivum. The ‘old’ standard wheat varieties (released between 1880 and 1950) suppressed the weed more than all the current varieties, with the exception of eight F1 hybrids. A doubling of the crop seeding rate of 10 of the genotypes in 1994 reduced the biomass of L. rigidum by an average of 25% compared with the standard seeding rate. Ranking of competitive ability of varieties at high density was consistent at both seeding rates. The strongly competitive genotypes had high early biomass accumulation, large numbers of tillers, and were tall with extensive leaf display. The potential for breeding enhanced competitive ability in wheat is discussed. [ABSTRACT FROM AUTHOR]

Fipronil seed treatments were evaluated to determine whether they directly influence germination and subsequent seedling growth in rice (Oryza sativa L). Continuous seed exposure to fipronil (four days) at 2000 mg litre-1 significantly impaired germination (P< 0.001). When exposure was restricted to a 1-h period 48h after the initiation of germination, early post-germination growth was also impaired(assessment two days after exposure, P<0.05). The proportion of seeds satisfying our criteria for normal germination fell by 2.3 and 2.6%respectively across 17 cultivars. Cultivar effects were highly significant (P<0.001). When exposure to fipronil (2000 mg litre-1) was restricted to 2h at initial seed wetting no significant growth impairment occurred. No significant differences (P > 0.05) were found between shoot lengths or root system dry weights of control plantsand plants developing from seed exposed continuously (two days) to fipronil at rates of up to 2000 mg litre-1 during germination and harvested nine days after sowing. Treating germinated seed with fipronil for 1 h immediately prior to sowing at rates of up to 4000mg litre-1 did not result in significant changes (P<0.05)in plant growth parameters at either nine or 25 days after sowing. No evidence of fipronil having a direct phytostimulatory effect on rice was obtained. [ABSTRACT FROM AUTHOR]