Determining the effectiveness of grazing and trampling by livestock in transmitting white clover mosaic and subterranean clover mottle viruses

Glasshouse and mini-sward experiments were done to determine the relative roles of grazing and trampling by livestock in transmitting white clover mosaic (WC1MV) and subterranean clover mottle (SCMoV) viruses between clover plants in pastures. Wounding due to grazing was simulated by repeatedly cutting plants with serrated scissors (glasshouse) or mowing (mini-swards), while wounding due to trampling was simulated by repeatedly bashing plants with the flat end of a wooden hammer handle (glasshouse) or rolling (mini-swards). In glasshouse experiments, cutting was more effective than bashing in transmitting WC1MV to white clover (Trifolium repens) plants but cutting and bashing transmitted it to subterranean clover (T. subterraneum) plants at similar rates. In an experiment with white clover mini-swards, mowing was more effective than rolling in transmitting WC1MV, and when both were combined, initially spread exceeded that obtained when the spread from mowing and rolling alone was added together. In glasshouse experiments, bashing was more effective than cutting in transmitting SCMoV to subterranean clover plants. In one experiment, neither mowing nor rolling spread SCMoV in mini-swards of subterranean clover. When transmission to subterranean clover cultivars which were ‘susceptible’ or ‘moderately susceptible’ to SCMoV was compared in glasshouse experiments, repeated bashing spread the virus more slowly to the ‘moderately susceptible’ cultivars. When mixed with ruminant saliva, infective sap containing WC1MV or SCMoV was still infective to clover plants after 4 wk storage at room temperature. When infective sap was allowed to dry naturally on a metal surface, SCMoV still infected clover plants when the dried sap was taken up in tap water after 4 but not 14 days, while WC1MV was infective after 24 h but not 4 days. These results suggest that grazing and mowing are more effective than trampling at transmitting WC1MV to white clover plants in pastures, while trampling is more effective at spreading SCMoV to subterranean clover. However, both transmitted WC1MV to subterranean clover at similar rates. Possible reasons for these differences are discussed in relation to differences in clover plant morphology and virus-specific factors.     

Changes in glucosinolates during crop development in single- and double-low genotypes of winter oilseed rape (Brassica napus): II. Profiles and tissue-water concentrations in vegetative tissues and developing pods

The concentrations of glucosinolates in the tissue water of leaves, stems, floral buds and developing pods were measured at defined stages of development in four oilseed rape cultivars known to have different seed glucosinolate concentrations (Bienvenu, Ariana, Cobra and Capricorn). Five alkenyl, two aromatic and three indolyl compounds were identified in the vegetative and reproductive organs. Substantial differences developed in the profiles of compounds present during vegetative growth. The 2-hydroxy-3-butenyl glucosinolate was primarily associated with developing and mature seeds and germinated seedlings. The 4-pentyl glucosinolate occurred mainly during the later stages of vegetative growth in spring, when leaves contained higher concentrations than stems, and during the early stages of flowering. The 2-phenylethyl and 3-indolymethyl glucosinolates were present earlier in vegetative growth when similar concentrations were present in leaves and stems. Differences between cultivars in the tissue-water concentrations of individual glucosinolates were small during vegetative growth. The leaves of Cobra and Capricorn had smaller concentrations of the 3-pentyl glucosinolate than Bienvenu and Ariana especially early in spring, and the stems of Capricorn had smaller concentration of the 3-pentyl and 2-phenylethyl glucosinolates. Greater differences between cultivars developed during pod growth and involved large increases in the concentrations of the 2-hydroxy-3-butenyl and 3-butenyl glucosinolates, especially in Bienvenu and Ariana. The implications of these changes in the types and concentrations of glucosinolates in the different organs for the incidence of pests and diseases are discussed.     

Mechanisms of energy dissipation in peanut under water stress

Effect of drought on the mechanisms of energy dissipation was evaluated in two-month-old Arachis hypogaea cvs. 57–422, 73–30, and GC 8–35. Plants were submitted to three treatments: control (C), mild water stress (S1), and severe water stress (S2). Photosynthetic performance was evaluated as the Hill and Mehler reactions. These activities were correlated with the contents of the low and high potential forms of cytochrome (cyt) b ₅₅₉, plastoquinone, cyt b ₅₆₃, and cyt f. Additionally, the patterns of carotenoids and chlorophylls (Chls), as well as the alterations of Chl a fluorescence parameters were studied. Under mild water stress the regulatory mechanism at the antennae level was effective for 57–422 and GC 8–35, while in the cv. 73–30 an overcharge of photosynthetic apparatus occurred. Relative to this cv., under S1 the stability of carotene and the dissipative cycle around photosystem (PS) 2 became an important factor for the effective protection of the PS2 reaction centres. The cyclic electron flow around PS1 was important for energy dissipation under S1 only for the cvs. 57–422 and 73–30.     

Changes in glucosinolates during crop development in single- and double-low genotypes of winter oilseed rape (Brassica napus): I. Production and distribution in vegetative tissues and developing pods during development and potential role in the recycling of sulphur within the crop

The distributions of glucosinolates and sulphur were measured in the vegetative and reproductive tissues in a series of single- and double-low cultivars of oilseed rape (Bienvenu, Ariana, Cobra and Capricorn) grown on a sulphur-sufficient soil at Rothamsted in 1987/88, and in crops of the cv. Libravo grown with none or 40 kg/ha of sulphur on a sulphur-deficient soil at Woburn in 1990/91. The glucosinolate measurements demonstrated large differences in the abilities of single- and double-low cultivars to synthesise glucosinolates, and showed that the biosynthetic differences were associated more with the developing pods than the vegetative tissues. It indicated that potential contribution of intact glucosinolates from vegetative tissues to the seed was likely to be small, but did not preclude the possibility that the vegetative tissues were a source of glucosinolate precursors. The sulphur measurements showed that the glucosinolates contained only a small proportion of the crop's total sulphur and that they were unlikely to be a major source of recyclable sulphur, even under conditions of severe sulphur deficiency.     

Differential responses to K deficiency among soybean cultivars

The seed yield per unit of potassium applied differed for five soybean cultivars which were grown to maturity under different K regimes in a glasshouse. Whereas Dodds was the most responsive cultivar to moderate increases in K supply, the cultivar Bragg was the most efficient in its ability to produce seed with low levels of available K; Lee and Forest were the least efficient cultivars while Bossier and Dodds were of intermediate efficiency. The basis for the efficiency of cv. Bragg was that the growth of its tops, as indicated by mature stem weights and its roots, were less affected by reduced K supply than those of other cultivars. This enabled it to produce more pods under K-deficient regimes, resulting in a greater seed yield per plant. The percentage reduction in oil/protein ratios in the seed of the five cultivars under moderate K deficiency correlated closely with reductions in seed yield. However, changes in this ratio were poorly related to the K percentages in the seed. All cultivars experienced an impairment of plant senescence under K deficiency as evidenced by a reduction in leaf abcission and a delay in pod maturity. The existence of genetic diversity in K-use efficiency means that breeding programmes could utilize K-efficient germplasm in developing new cultivars for soils not naturally high in potassium.     

STUDIES OF THE MICROPROPAGATION OF FOUR ZANTEDESCHIA CULTIVARS

Four Zantedeschia cultivars, namely "Golden Calla", "Pixie", "Pink Persusion" and "Black Magic", were used for this study. By ouly changing the oncentration of zeatin in Murashinge and Skoog mineral medium, good results of micropropaga-tion of Zantedeschia can be achieved even without any other rooting Phytohormone in the medium. The basic steps and the medium are given out as follows: l) shoot multiplication by adding 1 to 3mg/L of zeatin to MS medium; 2) shoot elongation by adding 0.2 to 0.4 mg/L zeatin into MS medium; 3) rooting by adding 0.05 to 0.2mg/L zeatin to MS medium.     

An endogenous growth inhibitor, 3-hydroxy-β-ionone. II. Changes in its levels associated with the light-induced growth inhibition of hypocotyls of Phaseolus vulgaris

Dark-grown, 4-day-old seedlings of dwarf bean ( Phuseolus vulgaris L. cv. Morocco) and tall bean (cv. Kentucky Wonder) were transferred to conditions of continuous light at various fluence rates, and the resulting changes in growth rates and concentration of 3-hydroxy-β-ionone, a novel endogenous growth inhibitor, were monitored. The light-induced inhibition of growth and the levels of the inhibitor concentration were dependent on the fluence rate of light applied. The growth rate of hypocotyls of both cultivars decreased rapidly and reached a plateau 18 h after the onset of light. However, the more noticeable changes were the marked inhibition of growth of the hypocotyls of the dwarf cultivar. The concentration of 3-hydroxy-β-ionone in the hypocotyls of both cultivars increased after a 20-min lag and reached plateau values after 12 h. The concentration of the inhibitor in the hypocotyls of the dwarf cultivar increased to about 4 to 8 times the level in the nonirradiated controls, while that in the hypocotyls of the tall cultivar increased only about 2- to 3-fold under the same conditions. The high concentration of 3-hydroxy-β-ionone in the dwarf cultivar under steady-state conditions in continuous light, as compared with that in the tall cultivar, may determine the growth habit of these cultivars.     

Midday photoinhibition of two newly developed super-rice hybrids

Super-rice hybrids are two-line hybrid rice cultivars with 15 to 20 % higher yields than the raditional three-line hybrid rice cultivars. Response of photosynthetic functions to midday photoinhibition was compared between seedlings of the traditional hybrid rice (Oryza sativa L.) Shanyou63 and two super-rice hybrids, Hua-an3 and Liangyoupeijiu. Under strong midday sunlight, in comparison with Shanyou63, the two super-rice hybrids were less photoinhibited, as indicated by the lower loss of the net photosynthetic rate (P _N), the quantum yield of photosystem 2 (Φ_PS2), and the maximum and effective quantum yield of PS2 photochemistry (F_v/F_m and F_v′/F_m′). They also had a much higher transpiration rate. Hence the super-rice hybrids could protect themselves against midday photoinhibition at the cost of water. The photoprotective de-epoxidized xanthophyll cycle components, antheraxanthin (A) and zeaxanthin (Z), were accumulated more in Hua-an3 and Liangyoupeijiu than in Shanyou63, but the size of xanthophyll cycle pool of the seedlings was not affected by midday photoinhibition. Compared to Shanyou63, the super-rice hybrids were better photoprotected under natural high irradiance stress and the accumulation of Z and A, not the size of the xanthophyll pool protected the rice hybrids against photoinhibition.     

How does a predator find its prey? Nesidiocoris tenuis is able to detect Tuta absoluta by HIPVs

The Zoophytophagous predator, Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is one of the most important candidates for controlling Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato crops. This predator uses different signals including morphological plant traits, prey insects, and volatile substances produced by the infested plants and prey signals to find its suitable prey. These signals are different in each cultivar of a plant. We aimed to understand how N. tenuis finds its prey using volatiles from tomato plants damaged or infested with T. absoluta. The predator’s responses to various plant treatments on two cultivars of tomato plants were tested in a flight tunnel and a four-choice olfactometer. The volatile compounds released from the treatments were also collected and identified. The results of the olfactory experiments showed that the predators even in the absence of light chose the plants bearing their insect prey. This behavior was not the same in both cultivars, and N. tenuis had a tendency toward mechanically damaged of Early Urbana Y cultivar more than Cal JN3 cultivar. The differences in the amount of monoterpenes, sesquiterpenes, and eugenol between cultivars may play a role in the differential attraction of N. tenuis towards infested plants. The difference in the volatile compounds was evident in two cultivars, and this was consistent with our bioassay results. Therefore, the choice of appropriate cultivar and use of herbivore-infested plant volatiles are important for developing a control strategy against T. absoluta and attract its predators.