Silicon amendment improves wheat defence against Fusarium graminearum and complements the control by fungicide of Fusarium head blight

A three-year field experiment with two wheat cultivars evaluated the effect of soil-applied silicon (Si), with and without fungicide spraying, on Fusarium head blight (FHB) control. Silicon treatment alone reduced FHB severity and the percentage of damaged wheat kernels, regardless of the cultivar. The best disease control was obtained for the cultivar with moderate disease resistance (MR), supplied with silicon and treated with fungicide during flowering. Silicon treatment alone promoted an increase in deoxynivalenol (DON) concentration in the disease-susceptible cultivar; however, in the MR cultivar, silicon amendment associated with fungicide treatment led to a reduction in DON concentration. Greenhouse experiments evaluated the effect of silicon combined with different timings of fungicide application on wheat defences against Fusarium graminearum. Plants supplied with silicon had a longer pathogen incubation period, lower FHB severity and lower DON concentration when compared to plants without silicon. In addition, silicon-supplied plants had higher soluble phenolic content and altered antioxidant enzyme activities (SOD, CAT, POX and PPO) that favoured early accumulation of hydrogen peroxide when compared to plants without silicon. Greater control of FHB and lower DON concentration in plants treated with silicon and fungicide before inoculation and up to 1 day after inoculation was associated with increased levels of defence-associated metabolites. Silicon contributed to the reduction of FHB and DON concentration in wheat, especially for the MR cultivar and, when combined with fungicide spraying, both MR and disease-susceptible cultivars had enhanced performances upon silicon amendment.     

Phylogeny,distribution and pathogenicity of Lasiodiplodia species associated with dieback of table grape in the main Brazilian exporting region

Botryosphaeria dieback is an important disease of table grape in the São Francisco Valley, the main Brazilian exporting region. The objectives of this study were to identify species of Lasiodiplodia associated with botryosphaeria dieback of table grapes in the São Francisco Valley, investigate the prevalence and distribution of the species in the region, and evaluate their pathogenicity and virulence in green shoots of table grape. A total of 112 Lasiodiplodia isolates were obtained from 14 vineyards, located in Casa Nova, Juazeiro and Petrolina. Fungal identifications were made using phylogenetic analysis based on partial sequences of translation elongation factor 1‐α (EF1‐α) and internal transcribed spacer (ITS) sequences, in combination with morphometric characteristics of conidia. Eight species of Lasiodiplodia were identified: L. brasiliense, L. crassispora, L. egyptiacae, L. euphorbicola, L. hormozganensis, L. jatrophicola, L. pseudotheobromae and L. theobromae. Except for L. crassispora, L. pseudotheobromae and L. theobromae, all the other species are reported for the first time on grapevine worldwide. The distribution of Lasiodiplodia species differed between the three table grape populations of São Francisco Valley. All Lasiodiplodia species isolated in this study were present in the population of Casa Nova and Lasiodiplodia theobromae was the most prevalent. All species of Lasiodiplodia were pathogenic on detached green shoots of grapevine, with L. brasiliense being the most virulent.     

Inheritance of resistance to a Bacillus thuringiensis toxin in a field population of diamondback moth (Plutella xylostella)

Inheritance of resistance to the Bacillus thuringiensis Berl. CryIA(b) crystal protein was studied in Plutella xylostella L. (diamondback moth). A field population 50-fold more resistant to CryIA(b) than a control susceptible strain was used. Dose-mortality curves of the resistant population, the susceptible strain and the F₁ from the two reciprocal crosses were compared. Resistance transmission to the F₁ was dependent on the sex of the resistant progenitor. Sex ratio of the survivors to high doses of CryIA(b) in the F₁ of the two reciprocal crosses did not corroborate the preliminary hypothesis of resistance being due to a recessive sex-linked allele. Since, in a previous work, the loss of CryIA(b) binding capacity of resistant insects had been demonstrated, binding to midgut tissue sections from F₁ individuals was also analysed. The presence of binding in all of the F₁ preparations showed that, at least, a recessive autosomal allele was responsible for the loss of binding capacity in the resistant population.     

Identification and transmission of Piper yellow mottle virus and Cucumber mosaic virus infecting black pepper (Piper nigrum) in Sri Lanka

Sri Lankan black pepper with symptoms of yellow mottle disease contained a mixture of viruses: Piper yellow mottle virus (PYMV) particles (30 × 130 nm), Cucumber mosaic virus (CMV, 30 nm diameter isometric particles), and unidentified, isometric virus-like particles (30 nm diameter). An effective purification procedure is described for PYMV. Immunosorbent and conventional electron microscopy successfully detected badnavirus particles only when at least partially purified extracts were used. PYMV was confirmed as the cause of the disease, with the other two viruses apparently playing no part in producing symptoms. PYMV was transmitted by grafting, by the insect vectors citrus mealy bug ( Planococcus citri ) and black pepper lace bug ( Diconocoris distanti ), but not by mechanical inoculation or through seeds. The CMV isolate was transmitted to indicator plants by mechanical inoculation and by the vector Aphis gossypii , but not by Myzus persicae ; but neither mechanical nor insect transmission of CMV to black pepper was successful. A sensitive polymerase chain reaction assay was developed to detect PYMV in black pepper.     

Soybean drought-stressed plants impair Anticarsia gemmatalis (Lepidoptera: Erebidae) midgut proteolytic activity and survival

Phytoparasitica - Soybean plants are exposed to multiple stresses during development. Co-occurring stresses can activate common defense pathways on plants, increasing end products concentrations,...     

Chemical and environmental factors driving germination of Solanum americanum seeds

Solanum americanum Mill. is a weed that occurs with a number of crops, and it is known for its high seed production and its staggered germination. The objective of this work was to evaluate the germination behavior of S. americanum seeds under the influence of chemical and environmental factors. In the laboratory, we tested the effect on germination of (i) constant and alternating temperatures, (ii) seed washing, (iii) exposure time and concentration of chemical treatments and (iv) seeding depth and soil covered with plant residue on seedling emergence. The variables analyzed were germination percentage, germination rate index, seedling emergence and length of the seedlings. The results indicated that alternating temperatures are the main way to promote germination of S. americanum; however, chemical treatments can help to increase the germination percentage and rate index. There was no increase in germination with seed washing, with the exception of KNO₃ application. A GA₃ concentration of 0.84 g L^?1 and an exposure time of 21.22 h in 0.2% of KNO₃ promoted the highest germination of S. americanum. Germination occurs when seeds remain on the soil surface and are not covered by crop residue.     

Absorption,translocation and metabolism of aminocyclopyrachlor in young plants of Ipomoea purpurea and Ipomoea triloba

Members of the Convolvulaceae family are known to be sensitive to aminocyclopyrachlor, although little is known about the absorption, translocation and metabolism of the herbicide in these species of weed. The aim of this study was to evaluate the absorption, translocation and metabolism of ¹⁴C‐aminocyclopyrachlor in young plants of Ipomoea purpurea and Ipomoea triloba. Assessments were performed at 3, 6, 12, 24, 48 and 72 h after treatment (HAT) for the study of absorption and translocation. Metabolism was assessed at three time points (3, 24 and 72 HAT). In terms of absorption, was observed a difference between species at the 3 and 48 HAT time points, where I. purpurea had a higher absorption of ¹⁴C‐aminocyclopyrachlor. No differences were observed between species at any other time points. Of the total absorbed herbicide, 90.9% for I. purpurea and 91.8% for I. triloba were detected on the treated leaf. I. purpurea presented higher translocation to the leaf above the treated leaf, while I. triloba showed higher translocation to the lower leaves and roots. No increase in absorption of ¹⁴C‐aminocyclopyrachlor was observed above 24 HAT for I. purpurea and above 6 HAT for I. triloba, and translocation was low (<1%) for both species in all plant parts. This suggests that post‐emergence application of aminocyclopyrachlor cannot be effective for the control of I. purpurea and I. triloba and alternative approaches are required. Nevertheless, no ¹⁴C‐aminocyclopyrachlor metabolites were observed in the studied plants, which indicated sensitivity in I. purpurea and I. triloba to the herbicide.