Photodynamic herbicides: 1. Concept and phenomenology

A new approach to the design of conceptually and phenomenologically new herbicides is described. It involves the joint utilization of tetrapyrrole precursors, such as δ-aminolaevulinic acid (a biodegradable amino acid) and activators of the chlorophyll biosynthetic pathway, such as 2,2′-dipyridyl, in order to induce treated plants to biosynthesize and accumulate massive amounts of tetrapyrrole intermediates of the chlorophyll biosynthetic pathway in the dark (i.e. at night). During the subsequent light period (daylight) the accumulated tetrapyrroles act as potent photodynamic sensitiziers, which in turn result in the death of susceptible plants in a matter of hours. We have therefore proposed to name herbicides that act via this mechanism as photodynamic herbicides, or more pictorially as laser herbicides. From a limited survey of agricultural plant and weed species it appears that photodynamic herbicides exhibit a very pronounced organ, age and species-dependent selectivity. For example, dicotyledonous weeds such as mustard, red-root pigweed, common purslane and lambsquarter are very susceptible while monocotyledonous plants such as corn, wheat, barley and oats are not. The biochemical basis of this selectivity seems to lie, among other things, in the rates of tetrapyrrole turnover and in a differential enhancement by the applied chemicals of the monovinyl and divinyl tetrapyrrole biosynthetic pathways in the various species. A survey of various groups of chemicals (herbicides and other selected biochemicals) that are likely to exhibit photodynamic herbicidal properties is currently under investigation.     

Rice response to inoculation with N2-fixing and P-solubilizing microorganisms

Summary Inoculation effect ofA. chroococcum, P. striata andA. awamorii on yield and nutrients uptake in rice was studied under green house conditions. The organisms appreciably increased the yield and uptake of nutrients with or without chemical fertilizers. Phosphorussolubilizing microorganisms and a mixture of the three showed better response than the rest of the treatments among single and mixed culture inoculations respectively. Chemical fertilizers further improved the yield and nutrients uptake. The yield response remained unaffected by replacing superphosphate with rock phosphate and microbial inoculations.     

Nitrogen fixation (C2H2 reduction) in soil samples from rhizosphere of rice grown under alternate flooded and nonflooded conditions

Summary In a greenhouse study the influence of alternate flooded and nonflooded conditions on the N₂-ase activity of rice rhizosphere soil was investigated by C₂H₂ reduction assay. The soil fraction attached to roots represent the rhizosphere soil. Soil submergence always accelerated N₂-ase and this effect was more pronounced in planted system. Moreover, rice plant exhibited phase-dependent N₂-ase with a maximum activity at 60 days after transplanting. The alternate flooded and nonflooded regimes resulted in alterations of the N₂-ase activity. Thus, the N₂-ase activity increased following a shift from nonflooded to flooded conditions, but the activity decreased when the flooded soil was returned to nonflooded condition by draining. However, the differential influence of the water regime on N₂-ase was not marked in prolonged flooded-nonflooded cycles. Microbial analysis indicated the stimulation of different groups of free-living and associative N₂-fixing microorganisms depending on the water regime.     

水稻雄核发育途径及游离花粉粒培养的活体观察

(1)在水稻雄核发育中,观察到 A—V、A—G、A—GV 和 B 途径,通常 B 途径占优势。在雄核发育早期,各种发育途径的花粉均有退化现象发生。(2)观察和统计表明,游离核型的多核花粉在发育过程中可转变为多细胞花粉,因而也是有发育前途的。(3)能够启动雄核发育的花粉通常是原生质稠密,在花粉群体中属中等大小(35—40μ)的花粉。多细胞花粉在突破花粉壁前。其细胞壁常常加厚,破壁时整个花粉有突然收缩的现象。(4)多细胞花粉内通常含有一些缓慢运动的小淀粉粒,它们可能积极参与了花粉雄核发育过程中的代谢活动。     

Concentration of iron and manganese in rice plants as influenced by hexachlorocyclohexane applied to soil

Summary Application of a granular formulation of hexachlorocyclohexane (HCH) to the potted soil at flooding decreased the concentration of iron and. to some extent, manganese in rice plants, especially at concentrations above 3 ppm active ingredient (a.i.) Likewise, HCH, applied to rice fields at transplanting (several days after submergence) caused a significant decrease in the concentration of iron, and not manganese, in the rice plant but only at concentrations above 12.5 kg a.i./ha despite high levels of reduced iron in the soil. Inhibition of iron reduction by HCH was more pronounced when applied at flooding than at several days after flooding.     

Effect of algal growth on the availability of phosphorus,iron and manganese in rice soils

Summary Laboratory experiments were conducted to study the effect of algal growth on the change of (I) pH, (II) available phosphorus and (III) solubility of iron and manganese content in five waterlogged alluvial rice soils of West Bengal, India. The results showed that the algal growth initially caused an increase in the soil pH, which later declined to the original value in some of the soils. The available phosphorus content decreased upto 90 days of their growth and began to increase towards the later period of incubation. The drastic fall of water soluble plus exchaneable manganese content of the soils due to algal growth was accompanied by similar increase in reducible manganese content. No appreciable change in water soluble plus exchangeable ferrous iron content was encountered but theN-NH₄OAC(pH 3) extractable iron due to algal growth progressively decreased with the progress of the incubation period.     

Effect of boron on the pollen vitality and yield of rice plants (Oryza sativa L. var. Jaya)

Summary Rice plants were grown in sand cultures with nutrient solution including boron at 0, 1, 2.5 and 5 ppm concentrations.In general, supply of boron improved the pollen vitality of rice flowers. It was stimulating up to 2.5 ppm concentration in the nutrient solution, beyond which (i.e., at 5 ppm) inhibitory effects appeared. The availability of boron also increased the yield of rice grains in the same order.Stimulating effects of boron may be linked with greater availability of sugars, increased enzymatic activity and respiration which favoured better growth of pollen. Inhibitory effects of stronger concentration of boron (5 ppm) may be related with physiological depression and injury to protoplasm itself.     

Biodegradation of rice stumps by soil mycoflora

Summary Cellulose and lignin contents in left-overs of rice stump decreased due to decay caused by soil mycoflora. The loss of cellulose and lignin was considerable in presence of Curvularia and Fusarium respectively. Other tested mycoflora could also destroy cellulose and lignin to some extent. The amount of loss of cellulose and lignin increased with time of incubation of the tested mycoflora.     

Genetic Evaluation and Utilization (GEU) program

Summary The Genetic Evaluation and Utilization (GEU) program of the International Rice Research Institute (IRRI) is an interdisciplinary program for the improvement of rice crops. Scientists trained in diverse disciplines such as plant breeding, plant pathology, entomology, agronomy, cereal chemistry, plant physiology, and soil chemistry work together and contribute their specialized skills to this joint endeavor. The program has five interrelated components: (1) germ plasm collection and conservation, (2) research in disciplinary areas, (3) development of improved germ plasm, (4) distribution, evaluation and exchange of germ plasm internationally, (5) training of young scientists.Over forty thousand rice varieties from different countries are being maintained in the IRRI germ plasm bank. These varieties have been screened for grain quality, resistance to various diseases and insects, and tolerance to various environmental stresses such as drought, high and low temperatures and problem soils. Donor parents for resistances to each of the problem areas have been identified. These parents were utilized for developing improved germ plasm. Varieties with resistance to as many as five diseases and five insect species have been developed. These multiple resistant varieties are grown on millions of hectares of rice land. Seeds of improved breeding materials are exchanged internationally and 194 scientists from different countries have been trained in rice improvement work.     

Mutagenic effectiveness and efficiency of EMS,DES and gamma-rays in rice

Summary Data on chlorophyll mutation frequency after treatment with EMS, DES and gamma-rays and sequential administration of gamma-rays and the two alkylating agents in three varieties of rice have been used to work out quantitatively the effectiveness and efficiency of each mutagen and combination treatment. For effectiveness, the order is EMS > DES and for efficiency it is EMS > DES > gamma-rays. In some sequential treatments (Gamma-rays + DES in IR8 and Basmati; DES + gamma-rays in IR8 and Jhona; Gamma-rays + EMS in IR8 and Basmati; and EMS + gamma-rays in IR8, Jhona and Basmati) mutation frequency is more than additive (synergistic) but these treatments are decisively less efficient because of their relatively high injurious effects in the M₁. generation. EMS induces more albinas than gamma-rays do. The mutational spectrum patterns induced by gamma-rays and DES are alike. In general, combination treatments tend to increase the frequency of albinas over other types of chlorophyll mutants.