Aqueous extracts of Artemisia frigida leaf and stem and soils beneath A. frigida were used to test their allelopathic effects on the seed germination and seedling growth of three Poaceae plants ...(Leymus chinensis, Stipa krylovii, and Cleistogenes squarrosa) on Leymus chinensis grassland. The aqueous extracts of A. frigida leaf and stem decreased the seed germination index of test plants and prolonged their seed germination time, and inhibited the shoot growth of the three plants and the root growth of S. krylovii. The aqueous extracts at concentration > or = 0.075 g x ml(-1) presented a strong inhibition on the root growth of L. chinensis, while those at concentration < or = 0.05 g x ml(-1) had less effects. For the root growth of C. squarrosa, the aqueous extracts showed a "low-promotion and high-inhibition effect". Under the effects of A. frigida soil, the seedling growth of test plants was inhibited. The sensitivity of test plants to the allelopathic effects of A. frigida was in the order of S. krylovii > L
Melaleuca quinquenervia (Cav.) S.T. Blake (Myrtales: Myrtaceae) forms dense monocultures that displace native vegetation in wetlands of southern Florida, USA. Faunal studies in the tree's native ...Australian range revealed several prospective biological control agents, including the leaf-blotching bug, Eucerocoris suspectus Distant (Hemiptera: Miridae). This herbivore was imported into quarantine to assess risk to Florida native and ornamental species after preliminary Australian studies had indicated that it might be useful. Ornamental Melaleuca spp. suffered heavy feeding in no-choice adult feeding trials, with moderate feeding on some native Myrtaceae. Native species sustained light to heavy feeding in multichoice adult feeding trials and in a no-choice nymphal feeding trial. Feeding increased on native species in a large enclosure after M. quinquenervia was cut, allowed to dry, and then removed. Nymphs completed development only on M. quinquenervia and ornamental bottlebrushes, Melaleuca spp. However, inability to fully develop on non-target species is of limited importance as a criterion for release of insects with highly mobile immature stages as compared to less vagile species. Local movement from the host to other plant species could result in unacceptable non-target damage despite seemingly adequate developmental specificity. This insect would clearly harm native and ornamental Myrtaceae and should therefore not be released.
Some herbivorous insect taxa that exhibit otherwise conservative patterns of host association include species or populations with atypical host specificities. These species provide special ...opportunities to study the evolution of host range. Uroleucon ambrosiae aphids present an example. Most Uroleucon species are monophagous on particular host plants from the Asteraceae, and U. ambrosiae appears to specialize on the giant ragweed, Ambrosia trifida, in eastern North America. In the American Southwest, however, U. ambrosiae uses a variety of asteraceous taxa as hosts. For the present study, we assayed host-associated behaviors of U. ambrosiae from both eastern and southwestern regions of the United States on each of four asteraceous genera. Data from choice and no-choice experiments and electrical penetration graph analyses revealed highly significant differences in the acceptability of the four test plants. Plant taxa were ranked in the same order across multiple behavioral assays by aphids from both regions. However, eastern and southwestern aphids exhibited significantly different patterns of behavior. Ambrosia was the most highly accepted plant by aphids from both regions, but southwestern aphids accepted the other test plants more readily than did eastern aphids, indicating geographic variation in degree of host specificity. This regional differentiation held for aphids reared under controlled conditions for the EPG studies, indicating a genetic basis for population divergence in U. ambrosiae host-use traits. We speculate that the generalism within U. ambrosiae is an evolutionarily derived trait and represents an ecological adaptation to the scattered and unpredictable distribution of the preferred A. trifida host in the arid American Southwest.
Volatility and drift are problems commonly associated with auxin-like herbicides. Field and greenhouse studies were conducted at Texas A & M University to develop a method of quantifying volatility ...and subsequent off-target movement of 2,4-D, dicamba, and triclopyr. Rate-response curves were established by applying reduced rates ranging from 4 × 10-1to 1 × 10-5times the normal use rates of the herbicides to cotton and soybean and recording injury for 14 d after treatment (DAT) using a rating scale designed to quantify auxin-like herbicide injury. Injury from herbicide volatility was then produced on additional cotton and soybean plants through exposure to vapors of the dimethylamine salt of 2,4-D, diglycolamine salt of dicamba, and butoxyethyl ester of triclopyr using air chambers inside a greenhouse and volatility plots in the field. Injury resulting from this exposure was evaluated for 14 d using the same injury-evaluation scale that was used to produce the rate-response curves. Volatility-injury data were then applied to the rate-response curves so that herbicide rates corresponding with observed injury could be calculated. Using this method, herbicide volatility rates estimated from greenhouse-cotton injury were determined to be 3.0 × 10-3, 1.0 × 10-3, and 4.9 × 10-2times the use rates of 2,4-D, dicamba, and triclopyr, respectively. Greenhouse-grown soybean developed injury consistent with 1.4 × 10-2, 1.0 × 10-3, and 2.5 × 10-2times the normal use rate of 2,4-D, dicamba, and triclopyr, respectively. Under field conditions, cotton developed injury symptoms that were consistent with 4.0 × 10-3, 2.0 × 10-3, and 1.25 × 10-1times the recommended use rates of 2,4-D, dicamba, and triclopyr, respectively. Field soybean displayed injury symptomology concordant with 1.6 × 10-1, 1.0 × 10-2, and 1.1 × 10-1times the normal use rates of 2,4-D, dicamba, and triclopyr, respectively. This procedure provided herbicide volatility rate estimates that were consistent with rates and injury from the rate-response injury curves. Additional research is needed to ascertain its usefulness in determining long-term effects of drift injury on crop variables such as yield.
Heliococcus bohemicus Sulc is very frequently found in vineyards in Northern Italy, where grapevine leafroll is widespread. Grapevine leafroll-associated virus 1 (GLRaV-1) and Grapevine ...leafroll-associated virus 3 (GLRaV-3) are also quite frequently observed, often in association with Grapevine virus A (GVA). The capacity of the mealybug to transmit these viruses to grapevine was therefore evaluated. Virus-free insects were fed on infected vines and then transferred to healthy test-plants. GLRaV-3 was transmitted to two out of 77 test-plants and GVA to one out of 38; GLRaV-1 was not transmitted. This is the first report of GVA transmission by H. bohemicus and the first report of the capacity of this mealybug to transmit GLRaV-3 to grapevine in Italy
Heliococcus bohemicus Sulc. si ritrova frequentemente nei vigneti in Italia Settentrionale, dove è diffuso l'accartocciamento della vite. Il Virus 1 associato all'accartocciamento della vite (GLRaV-1) e il Virus 3 associato all'accartocciamento della vite (GLRaV-3) sono pure osservati di frequente, spesso in associazione con il Virus A della vite (GVA). E' stata perciò valutata la capacità della cocciniglia di trasmettere questi virus alla vite. Insetti esenti da virus sono stati alimentati su piante infette e poi trasferiti su piante test sane. GLRaV-3 è stato trasmesso a due di 77 piante test e GVA a una di 38; GLRaV-1 non veniva trasmesso. Questa è la prima segnalazione della trasmissione di GVA da parte di H. bohemicus e la prima segnalazione della capacità di questa cocciniglia di trasmettere GLRaV-3 alla vite in Italia.
The aim of our work was to demonstrate the effects of digestate application as a nutrient source on crop yield, on the inside content value of test plant and on soil physico-chemical and biological ...parameters. The digestate was used at the rates of 0, 5 and 10 L m-2, two times in the vegetation period for soybean test plant. We measured different yield components, oil and protein content and amino acid composition of soybean, collected from three square meters from each plots. We measured the general soil physico-chemical parameters and invertase, dehydrogenase, catalase activities as well as the number of different groups of soil microbes by modified plate dilution technique. Our results show, that digestate application has not caused drastic changes in soil properties, but it was very favourable as a nutrient source. It increased significantly the crop yield of treated soybean and also increased the protein and amino acid content of the test plant. Biogasdigestate could be become a very useful material for plant nutrition.
xperimental transmission of European stone fruit yellows phytoplasma to Japanese plum cv. "Ozark Premier" was achieved using Cacopsylla pruni, caught in the field or raised on infected plants under ...controlled conditions. Using different groups of infectious psyllas, 89% of the inoculated test plants were infected. Both nymphs and adults were able to transmit. Insects exposed to test plants immediately after capture or raised in cages transmitted the disease. After an incubation period of 4-5 months the first test plants showed typical symptoms. Sources of inoculum, test plants and vectors were examined by PCR for the presence of phytoplasmas. Following digestion of the amplification products with restriction enzymes, isolates from plants and insects showed the same restriction profiles. Interestingly, pear decline and European stone fruit yellows, members of the apple proliferation cluster, are both transmitted by Cacopsylla spp
The presence and colonisation step of apple proliferation phytoplasma in recovered, symptomatic and never symptomatic apple trees were studied. Using serological and molecular techniques, it was ...demonstrated that recovered plants maintain infectivity in their roots, while they lose phytoplasmas from shoots and leaves; in contrast, apple proliferation symptomatic trees are completely colonised. Several plants that showed no apple proliferation symptoms during twelve years of observation were found to be infected in their roots. Graft transmission experiments with apple proliferation phytoplasma, using both roots and buds collected from donor recovered and symptomatic trees, confirmed the results obtained by the analyses. The graft-inoculated plants did not recover and symptom severity was not influenced by the source of inoculum. To determine the health status of the apple trees as regards apple proliferation the roots must be tested
Sono state studiate la presenza e la fase di colonizzazione del fitoplasma degli scopazzi del melo in piante di melo guarite, sintomatiche e mai sintomatiche. Utilizzando tecniche sierologiche e molecolari, è stato dimostrato che le piante guarite mantengono l'infettività nelle radici, mentre perdono i fitoplasmi nei rami e nelle foglie; al contrario, le piante che presentano i sintomi degli scopazzi sono colonizzate completamente. Numerose piante che non hanno presentato sintomi di scopazzi nel corso di dodici anni di osservazioni sono risultate infettate nelle radici. Esperimenti di trasmissione tramite innesto del fitoplasma degli scopazzi, utilizzando radici e gemme prelevate da piante guarite e da piante con sintomi, hanno confermato i risultati ottenuti dalle analisi. Le piante inoculate tramite innesto non guarivano e la gravità dei sintomi non era influenzata dalla fonte dell'inoculo. Per determinare lo stato di salute delle piante di melo nei riguardi degli scopazzi si devono sottoporre a controllo le radici
Allelopathy of three spreading, noxious weed species (velvetleaf –Abutilon theophrastiMedic., jimsonweed –Datura stramoniumL., cocklebur –Xanthium italicumMor.) were studied in 2008. These species ...can impose their allelopathy on other plants, but in many cases investigators can their different effects in several experiments, so their real allelopathic effects are questionable. Some investigators suggested that several environmental (abiotic and biotic) factors may play role in allelopathic relationships, and can modify it significantly. Effect of drought stress and temperature were studied on allelopathy of the three weeds imposed on test plants (cress –Lepidium sativum). Germination and growth of test plant were evaluated, and concentrations of some allelochemicals were measured in donor plants. It was found that all examined environmental factors had significant effect on allelopathy of velvetleaf, jimsonweed and cocklebur appeared in responses of test plant and amounts of allelochemicals.
Previous work has shown that the contact inhibition that occurs among roots of Ambrosia dumosa shrubs has a self/ nonself recognition capability. In the current study, we investigated some of the ...geographic and genotypic dimensions of this recognition capability by using root observation chambers to observe the effects of encounters of individual roots on root elongation rates. We measured such effects in encounters between roots of plants from the same region and compared these to effects in encounters between roots of plants from two different regions. We also measured effects of encounters between roots of plants from the same clones and compared these to effects of encounters of roots of plants from different clones. Roots of plants from the same region (population) showed the usual "nonself" precipitous decline in elongation rates following contact, but when roots of plants from different regions contacted each other, elongation rates continued unchanged. When roots of separate plants from the same clone contacted each other, the same "nonself" precipitous decline in elongation rates as seen in encounters between roots of plants of different clones from the same region occurred. Meanwhile, in these same experiments "self" contacts between sister roots connected to the same plants resulted in no changes in elongation rates. Thus, differences between individuals from two geographically separate populations of Ambrosia dumosa may be sufficient to thwart the "nonself," population-level recognition of similarity apparently necessary for contact inhibition. Furthermore, the "self" recognition mechanism, which precludes contact inhibition between two roots on the same plant, appears to be physiological rather than genetic in nature.
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