Selection of herbicide-tolerant soybean cells and mechanism of tolerance to oxyfluorgen

Thesis (Ph.D. in Agriculture)--University of Tsukuba, (A), no. 1345, 1995.3.2

CLASSIFICATION OF POPULATION STRUCTURE FOR ALLELOPATHIC PROPERTIES IN ITCHGRASS (Rottboellia cochinchinensis)

Biodiversity of Rottboellia cochinchinensis from different areas were studied by morphological traits and amplified fragment length polymorphism (AFLP) analysis for classify of an allelopathic ability. The correlation of the similarity/distance between AFLP markers (Jaccard coefficient) and morphological traits (Euclidean distance) was significant with r = − 0.84**. Itchgrass could be divided into two groups from both UPGMA and STRUCTURE analyses: the group A consisted of itchgrass from Chaehom-Lampang, Si Thep-Phetchabun, Phrom Phiram-Phitsanulok, Amphur Muang-Nakhon Sawan, Kamalasai-Kalasin, Amphur Muang-Chachoengsao and Bang Yai-Nonthaburi, whereas itchgrass from Amphur Muang-Chiang Mai, Pak Chong-Nakhon Ratchasima and Kamphaeng Saen-Nakhon Pathom constituted the group B. Allelopathic properties of itchgrass as representative from different group were determined in bioassay test, the result showed that the aqueous extract of itchgrass from Chaehom-Lampang area has a strong allelopathic ability on growth of Echinochloa crus-galli L., Bidens pilosa L. and Lactuca sativa L. than the other group. The molecular analysis was strongly supported in morphological analysis clustering with bioassay test for allelopathic ability, specific morphological traits were soft trichomes, and the dark purple stems and roots which can be used for the preliminary classification of allelopathic ability. Our findings suggest that classification of itchgrass by morphological traits is related to the analysis of the genetic relationship of itchgrass with AFLP analysis, that allowing the assessment of the bio-diversity of itchgrass and their allelopathic potentials

Managing weeds using crop competition in soybean [Glycine max (L.) Merr.]

Soybean (Glycine max (L.) Merr.) is an important crop worldwide for both protein meal and vegetable oil. Soybean accounts for more than 50% of the global oilseed production. Weed infestation is a complex and regular threat to soybean production all over the world. To combat this threat, chemical, mechanical, and cultural methods are generally used. There has been a revived interest in weed suppression through improved crop competitiveness as an alternative aid in weed management. Different approaches could be utilized to increase crop competitiveness such as adjustment of row spacing, optimum seeding rate, and use of genotypes with high weed-competitive ability. During the past several decades, adoption of narrow row spacing has become increasingly popular among soybean growers primarily because of yield advantage and early canopy closure, which directly provides greater weed suppression. Adoption of narrow rows significantly reduces the density and biomass of late-season emerging weeds and delays the critical time for weed removal compared with wide rows. An increase in seeding density/plant population also suppresses weeds by earlier canopy closure, especially when combined with narrow row spacing. Competitive abilities of different soybean cultivars against different weed species are not consistent. Interseeding cover crops after establishment of soybean also can be a viable option for weed suppression as long as cover crops do not compete with soybean, or act as weeds themselves. Integrated weed management is considered to be the most effective approach for long-term and sustainable management of weeds in soybean. The objective of this article is to provide an overview of currently known cropping practices for improving soybean competitiveness against weeds