Growth patterns of cultivated rice varieties and weedy rices vary considerably. Pot experiments were conducted in an insect-proof house at the Institute of Advanced Studies, University of Malaya, Kuala Lumpur in 1993-1994 to evaluate allometric response and growth patterns of three selected strains of weedy rices (Oryza sativa L.) and a cultivated rice (O. sativa L. cv. MR84). Rice cv. MR84 was shorter than the weedy rices but produced more tillers/plant and greater total number of leaves/plant than weedy rice strains V26 and V27. Tillering and leaf production capacity of MR84 and weedy rice V69 were similar. Leaf and non-productive tiller mortality set in ca. 60 days after transplanting (DAT) for MR84 and ca. 30-50 DAT for weedy rites. Both leaf and tiller productions in MR84 and weedy rices exhibited a curvilinear pattern. The net population of number of leaves/plant showed normal quadratic function with time while that of tiller population/plant were sigmoidal, expressed in a generalized form of Y=e^t, where t=a+bx+cx² with meaningful variations in e^t values among the rices for both growth parameters. In the allometric partitioning of biomass, MR84 allocated more biomass to the roots with significantly (p<0.01) higher value of allometric coefficient (k) than the weedy strains. Both MR84 and V69 exhibited significantly higher RE values than V26 and V27. The total number of tillers of MR84 was similar to V27 but was significantly lower than V69 and V26. Grain yield of MR84 was ca. 7.88tons/ha and this was comparable to the respective yields of V26 and V27 but was significantly (p<0.01) lower than that of V69. The percentages of filled grain weight and unfilled grain weight/panicle were comparable, ranging from 83.4% for MR84 and 82.4-89.2% for weedy strains. MR84 registered significantly (p<0.01) heavier 1000 grains weight than the weedy accessions although their harvest indices were fairly similar.

View full abstract

Scirpus wallichii Nees and S. juncoides Roxb. var. ohwianus T. Koyama, which are dominant weeds in paddy fields in the northeastern region of Japan, were compared in terms of dormancy of seeds buried in paddy soil at Tohoku National Agricultural Experiment Station, Omagari, Akita, Japan. Wagner pots filled with paddy soil, in which seeds of both species were placed at the depths of 5 to 10cm, were buried in the paddy field. The seeds were recovered periodically to determine the germination ratio. The dormancy of seeds was estimated based on the germination percentage under four temperature conditions, 15, 20, 25 and 30°C.
1. The awakening of seeds of both species in the paddy soil from the primary dormancy was promoted gradually from the time of burial in the autumn until rice transplanting in May. The germination percentage of seeds of both species decreased from June to October. Induction of secondary dormancy reflected by a decrease in the germination percentage was more conspicuous in S. juncoides than in S. wallichii. Awakening of seeds of both species from the secondary dormancy began in November (Fig. 1).
2. The depth of the dormancy in seeds of S. juncoides at the time of rice transplanting varied among the years, while that of S. wallichii was not as conspicuous as that of S. juncoides (Table 2). The difference in the degree of dormancy of seeds of S. juncoides at the time of rice transplanting was attributed to the difference in the depth of the primary dormancy.

View full abstract

When cucumber seeds were sown on agar containing L-3, 4-dihydroxyphenylalanine (L-DOPA), the growth of cucumber seedlings was strongly inhibited by L-DOPA immediately after sowing. However, they recovered from the inhibitory effect of L-DOPA 12 days after sowing. Throughout the experimental period, blacking of agar was observed in the medium containing L-DOPA due to chemical alteration of L-DOPA in agar associated with a polymerization reaction. In the roots of cucumber seedlings treated with L-DOPA, accumulation of L-DOPA and free amino acids was observed compared with the control. Especially, the amount of tyrosine and phenylalanine with a similar chemical structure to that of L-DOPA increased remarkably.
It was assumed that the increase was due to the metabolim of L-DOPA to other harmless amino acids. This transformation of L-DOPA could be one of the detoxification mechanisms responsible for the recovery from the inhibitory effects of L-DOPA.

View full abstract

N, N-dialkyl-3-substituted phenylthio-1H-1, 2, 4-triazole-1-carboxamide derivatives were synthesized and their herbicidal activity and selectivity were evaluated by pot tests in a greenhouse.
1. Pre-emergence herbicidal activity and selectivity under paddy conditions.
The introduction of a lower alkyl group, and chloro atom at the 2, 6 positions on the benzene ring enhanced the herbicidal activity without adverse effect on transplanted rice. The substitutions of 2, 6-dimethyl, 2-methyl-6-ethyl, 2-methyl-6-chloro, and 2, 4, 6-trimethyl on the benzene ring resulted in the strongest herbicidal activity against Echinochloa oryzicola Vasing., among the tested compounds. The selectivity value between rice and Echinochloa oryzicola (ED₁₀ of rice/ED₉₀ of ECHOR) was 200 or more. The N, N-diethyl and N-ethyl, N-propyl derivatives on the carbamoyl moiety induced a higher herbicidal activity than the other alkyl-substituted derivatives. Sulfone linkage between the triazole and the benzene rings resulted in a higher herbicidal activity than sulfoxide or sulfide linkages (Table 1).
2. Post-emergence herbicidal activity under paddy conditions.
Post-emergence herbicidal activity against Echinochloa oryzicola in water application was evaluated for the selected compounds based on the results from pre-emergence application. Among them, N, N-diethyl-3-mesitylsulfonyl-1H-1, 2, 4-triazole-1-carboxamide (cafenstrole) showed the highest activity (Table 2).

View full abstract