Effect of environmental conditions on plant growth regulator activity of fungicidal seed treatments of barley

The triazole fungicide triadimenol is known to have plant growth regulator (PGR) activity in cereals when applied as a seed dressing. The effect of environmental conditions on PGR activity of triadimenol, other triazoles (flutriafol, prothioconazole, tebuconazole), the benzimidazole fuberidazole, imidazoles (imazalil, prochloraz), and the strobilurin fluoxastrobin on barley (Hordeum vulgare) was investigated using commercial seed dressings also including pyrimethanil (anilinopyrimidine) and triazoxide (benzotriazine), under controlled conditions. Irrespective of temperature or soil water content (SWC) triazole-containing seed treatments had a significant effect on the time and rate of plant emergence. Both triadimenolcontaining products significantly reduced the length of subcrown internodes and resulted in reduced shoot length three weeks after sowing. Growth suppression was stronger under optimal environmental conditions (17 to 19°C, 60 % SWC). Under suboptimal conditions – 9 to 10°C and 40 % SWC, respectively – no differences in shoot length were detected five weeks after sowing, whereas under optimal conditions plant growth retardation was still significant. The flutriafol-containing product partly inhibited shoot elongation, but never affected dry mass accumulation and root growth. The strobilurin-containing seed dressing had no marked plant growth activities on seedling emergence, shoot length and subcrown internode, but slightly stimulated root growth under all environmental conditions. The results indicate varying PGR activities of triazole seed dressings in response to mixing partner and growth conditions and suggest an increased stress tolerance of seedlings treated with triadimenol, enabling barley to better cope with suboptimal environmental conditions

Efficiency of self-cleaning properties in wheat (Triticum aestivum L.)

An experimental study was carried out to assess the efficiency of self-cleaning properties of three wheat cultivars and their potential in the protection against Blumeria graminis f. sp. tritici, a fungus that causes powdery mildew. Leaf samples with intact epicuticular structure were compared to such with wiped wax crystals. Contact angles were determined and the surfaces were subjected to a standardized contamination test with hydrophobic fluorescence powder. Another set of samples was inoculated with conidia of B. graminis and, after various time intervals, exposed to artificial fog or rain. For the intact surfaces of all cultivars contact angles of about 165° were measured. It is therefore suggested that wheat should be termed superhydrophobic. The wiping of the wax crystals led to a significant decrease of contact angles. This fact underlines the importance of surface roughness for achieving extreme water-repellency. In the standardized contamination test significantly more particles remained on the wiped surfaces than on those who had been left intact. This result was ascribed to increased adhesion on the smoothed samples.The inoculation with subsequent precipitation revealed a significantly better removal effect of conidia from intact than from wiped surfaces. This was irrespective of the wheat cultivar. In general, conidia were more effectively removed by rain than by fog. This was probably due to the higher kinetic energy and the greater amount of water when using rain. If fog application was delayed by 3 hours a higher percentage of conidia remained on the surface. As possible causes are discussed increased adhesion by conidia secretions or the development of primary germ tubes.Despite its highly efficient self-cleaning properties proved here, wheat is frequently infected by Blumeria graminis. We conclude that the high water content of the mildew conidia, the ability of Blumeria graminis to germinate at very low humidities and its rapid irreversible adhesion are effective adaptations in order to overcome the barrier of a superhydrophobic self-cleaning surface

Nuclear magnetic resonance: a tool for imaging belowground damage caused by Heterodera schachtii and Rhizoctonia solani on sugar beet

Belowground symptoms of sugar beet caused by the beet cyst nematode (BCN) Heterodera schachtii include the development of compensatory secondary roots and beet deformity, which, thus far, could only be assessed by destructively removing the entire root systems from the soil. Similarly, the symptoms of Rhizoctonia crown and root rot (RCRR) caused by infections of the soil-borne basidiomycete Rhizoctonia solani require the same invasive approach for identification. Here nuclear magnetic resonance imaging (MRI) was used for the non-invasive detection of belowground symptoms caused by BCN and/or RCRR on sugar beet. Excessive lateral root development and beet deformation of plants infected by BCN was obvious 28 days after inoculation (dai) on MRI images when compared with non-infected plants. Three-dimensional images recorded at 56 dai showed BCN cysts attached to the roots in the soil. RCRR was visualized by a lower intensity of the MRI signal at sites where rotting occurred. The disease complex of both organisms together resulted in RCRR development at the site of nematode penetration. Damage analysis of sugar beet plants inoculated with both pathogens indicated a synergistic relationship, which may result from direct and indirect interactions. Nuclear MRI of plants may provide valuable, new insight into the development of pathogens infecting plants below- and aboveground because of its non-destructive nature and the sufficiently high spatial resolution of the method

Fungal entomopathogens: new insights on their ecology

An important mechanism for insect pest control should be the use of fungal entomopathogens. Even though these organisms have been studied for more than 100 y, their effective use in the field remains elusive. Recently, however, it has been discovered that many of these entomopathogenic fungi play additional roles in nature. They are endophytes, antagonists of plant pathogens, associates with the rhizosphere, and possibly even plant growth promoting agents. These findings indicate that the ecological role of these fungi in the environment is not fully understood and limits our ability to employ them successfully for pest management. In this paper, we review the recently discovered roles played by many entomopathogenic fungi and propose new research strategies focused on alternate uses for these fungi. It seems likely that these agents can be used in multiple roles in protecting plants from pests and diseases and at the same time promoting plant growth

Prospects for plant defence activators and biocontrol in IPM - Concepts and lessons learnt so far

There is an urgent need to develop new interventions to manage pests because evolution of pesticide resistance and changes in legislation are limiting conventional control options for farmers. We investigated β-aminobutyric acid (BABA), jasmonic acid (JA) and fructose as possible plant defence activators against grey mould disease, . Botrytis cinerea, and root knot nematode, . Meloidogyne incognita. We also tested . Trichogramma achaeae parasitoid wasps and an antifeedant plant extract for biocontrol of the invasive tomato leafminer, . Tuta absoluta. BABA and JA enhanced resistance of tomato plants to . B. cinerea but neither treatment provided complete protection and the efficacy of treatment varied over time with BABA being more durable than JA. Efficacy was partly dependent on tomato cultivar, with some cultivars responding better to BABA treatment than others. Furthermore, treatment of tomato with BABA, JA and fructose led to partial suppression of . M. incognita egg mass development. Biocontrol agent, . T. achaeae, performance against . T. absoluta could be enhanced by adjusting the rearing conditions. Both attack rate and longevity were improved by rearing the parasitoids on . T. absoluta rather than on other insects. Finally, . Ajuga chamaepitys extract was shown to have significant antifeedant activity against . T. absoluta. Our findings suggest that there are potential new solutions for protection of crops but they are more complicated to deploy, more variable and require more biological knowledge than conventional pesticides. In isolation, they may not provide the same level of protection as pesticides but are likely to be more potent when deployed in combination in IPM strategies

Biosecurity and Yield Improvement Technologies Are Strategic Complements in the Fight against Food Insecurity

The delivery of food security via continued crop yield improvement alone is not an effective food security strategy, and must be supported by pre- and post-border biosecurity policies to guard against perverse outcomes. In the wake of the green revolution, yield gains have been in steady decline, while post-harvest crop losses have increased as a result of insufficiently resourced and uncoordinated efforts to control spoilage throughout global transport and storage networks. This paper focuses on the role that biosecurity is set to play in future food security by preventing both pre- and post-harvest losses, thereby protecting crop yield. We model biosecurity as a food security technology that may complement conventional yield improvement policies if the gains in global farm profits are sufficient to offset the costs of implementation and maintenance. Using phytosanitary measures that slow global spread of the Ug99 strain of wheat stem rust as an example of pre-border biosecurity risk mitigation and combining it with post-border surveillance and invasive alien species control efforts, we estimate global farm profitability may be improved by over US$4.5 billion per annum