Development of black dot disease (Colletotrichum coccodes (Wallr.) Hughes) and its effects on the growth and yield of potato plants

Seed tubers of cvs Désirée and Pentland Crown with different severities of black dot were planted in 1988 and 1989 at Rothamsted in fields in 4– or 7-course rotations, respectively. Tubers treated with prochloraz (1988) or imazalil (1989) were planted in some plots, and in others Colletotrichum coccodes inoculum was added to the soil at planting. In further experiments at Mepal, Cambridgeshire in 1989 and 1990 and at Rothamsted in 1990 on sites where potatoes had not been grown for more than 15 years, large amounts of inoculum were added to the soil around disease-free seed tubers of two (1989) or three (1990) cultivars at planting. In all experiments plants were sampled during the season and the effects of treatments on disease development, growth and yield were recorded. Disease on roots, stem bases and tubers was found early in the season and was more severe on Désirée than on Pentland Crown plants from fields in 4– or 7-course rotations. Severity increased throughout the season and with increasing amounts of disease on the seed tubers, especially with Desiree. Disease was also found on plants from disease-free tubers and was more severe in 1988 than 1989. At harvest, black dot on tubers was significantly more severe from severely affected than from disease-free seed, and was most severe where inoculum, especially large amounts, had been added at planting. Fungicide treatment decreased disease early in the season but had no effect on tuber infection at harvest. In 1989 the weight loss of seed tubers during sprouting increased with increasing amounts of black dot, but the disease had little effect on plant size through the season. At harvest the yield of ware tubers (>50 mm) decreased with severe disease but total tuber yields were not significantly affected. However, at harvest in 1988 severely affected seed yielded significantly less than healthy seed. Plants grown from mini-tubers were free from disease on sites where potatoes had not been grown for at least 15 years. Inoculum applied at planting caused severe disease on all cultivars in both years, whereas disease was slight on uninoculated plants. Inoculated plants senesced early at Mepal in 1990, but there were no significant differences in total tuber yield in any experiment. However, yields of ware tubers (>50 mm) were sometimes decreased and the total tuber number per plant increased.     

褐稻虱在武育粳2号上不同生育期危害对水稻产量结构的影响

通过试验测定在武育粳2号上水稻拔节期正处于幼穗形成阶段,受褐稻虱危害实粒数减少,产量下降;孕穗期较耐褐稻虱危害,有明显的补偿作用;孕穗末期至灌浆初期为水稻受害最敏感的时期,危害后使结实率和千粒重均明显下降,水稻显著减产;灌浆后期至乳熟期受褐稻虱危害主要导致干粒重降低,且越接近成熟产量损失越低。     

生态环境对白芷产量质量的影响

生态环境对白芷产量质量的影响陈兴福,丁德蓉,刘岁荣,卢进,黄文秀（四川省中医药研究院药物种植研究所,南川６４８４０８）ＥｆｆｅｃｔｏｆＥｃｏ－ＥｎｖｉｒｏｎｍｅｎｔｏｎＤａｈｕｒｉａｎＡｎｇｅｌｉｃａＹｉｅｌｄａｎｄＩｔｓＱｕａｌｉｔｙ￥ＣｈｅｎＸｉ...     

黄土丘陵沟壑区水平梯田改土培肥增产技术措施体系

黄土丘陵沟壑区水平梯田改土培肥增产技术措施体系刘东海赵廷宁（宁夏西吉县农业局７５６２００）（北京林业大学水土保持学院１０００８３）赵国杰（宁夏西吉县农业技术推广站７５６２００）ＴｅｃｈｎｉｑｕｅｓｏｆＳｏｉｌＩｍｐｒｏｖｅｍｅｎｔａｎｄＹｉｅｌｄＩｎ...     

Magnetic field dependence of radical-pair decay kinetics and molecular triplet quantum yield in quinone-depleted reaction centers

Radical-pair decay kinetics and molecular triplet quantum yields at various magnetic fields are reported for quinone-depleted reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides R26. The radical-pair decay is observed by picosecond absorption spectroscopy to be a single exponential to within the experimental uncertainty at all fields. The decay time increases from 13 ns at zero field to 17 ns at 1 kG, and decreases to 9 ns at 50 kG. The orientation averaged quantum yield of formation of the molecular triplet of the primary electron donor, ³P, drops to 47% of its zero-field value at 1 kG and rises to 126% at 50 kG. Combined analysis of these data gives a singlet radical-pair decay rate constant of 5 · 10⁷s^?1, a lower limit for the triplet radical-pair decay rate constant of 1 · 10⁸s^?1 and a lower limit for the quantum yield of radical-pair decay by the triplet channel of 38% at zero field. The upper limit of the quantum yield of ³P formation at zero field is measured to be 32%. In order to explain this apparent discrepancy, decay of the radical pair by the triplet channel must lead to some rapid ground state formation as well as some ³P formation. It is proposed that the triplet radical pair decays to a triplet charge-transfer state which is strongly coupled to the ground state by spin-orbit interactions. Several possibilities for this charge-transfer state are discussed.     

Field evaluation of symbiotic nitrogen fixation by rhizobial strains using15N methodology

Summary Small differences in N₂ fixation by nodulated soybeans (Glycine max. (L.) Merr.), inoculated with various strains ofRhizobium japonicum, were assessed in field experiments using¹⁵N methodology, and compared with yields of plant dry matter and total N. Percentage of plant-N derived from atmospheric N₂ and from fertilizer, and values of %¹⁵N atom excess had lower coefficients of variation than did total N and dry matter yield. Nevertheless the precision of estimates of kg N/ha fixed were sufficient to differentiate only the extremes of the range of strains tested, and there were discrepancies between ranking of strains based on % N derived from fertilizer and on total N yield.     

Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q⁻) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q⁻ than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680⁺ completely saturates, whereas that of carotenoid triplet continues to increase.

The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 10⁷ s⁻¹ at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.     

Yield components in Hevea brasiliensis– theoretical considerations

Abstract A theoretical analysis of yield components of Hevea brasiliensis is attempted in this paper. The effect of the major yield components, i.e. initial flow rate per unit length of tapping cut, length of the cut, percentage rubber content and plugging index on rubber yield is represented by the formula Variation in yield within and between clones can be ascribed to variation to any one of the above components. The importance of high growth rate for maintaining high yield throughout the life cycle of the tree is theoretically elucidated. While the present contention of a theoretical maximum yield of 9.5 t ha^?1 with a stand of 350 trees is questioned, the theoretical possibility of attaining that yield by increasing the stand per ha to 600 is analysed.     

A method for the determination of confidence limits for the P/2e − ratio for chosen values of Y ATP max from the results of continuous culture experiments

A model is described, which allows the determination of 95% confidence limits for the maintenance coefficient and the efficiency of oxidative phosphorylation for chosen values of the growth yield for ATP corrected for energy maintenance (Y _ATP ^max ). As experimental data the specific rates of substrate consumption, product formation and oxygen uptake in chemostat cultures at various growth rates are used.