Salinity is one of the major environmental constraints limiting agricultural productivity in the world. The effects of salt stress on growth, ions and organic solutes accumulation were investigated in two amaranth (Amaranthus cruentus) cultivars: Rouge (salt-resistant) and Locale (salt-sensitive). Young plants of these cultivars were exposed, in hydroponic system, to three concentrations of NaCl: 0, 30 and 90 mM. Growth parameters, ions, free proline and soluble sugars concentrations were determined after 2 weeks of stress. NaCl effect resulted in plant growth reduction in both cultivars but plants of cultivar Rouge were less affected compared to that of cv. Locale. Na + , proline How to cite this paper: Wouyou, A., Prodjinoto, H., Zanklan, A.S., Vanpee, B., resistance in these cultivars and that soluble sugars may play an important role in salt-resistance in Amaranthus cruentus. However, proline appears as a symptom of injury in stressed plants rather than an indicator of resistance.
The host range of Polymyxa graminis isolates originating from peanut clump-infested areas in India (Andhra Pradesh and Rajasthan), Pakistan and Senegal was studied on monocotyledonous and dicotyledonous cultivated species, using known quantities of sporosori as inoculum. Profuse multiplication occurred only on some graminaceous species, but the various isolates showed different host specificity. All the isolates produced high infection on sorghum and pearl millet, and all but one isolate from Rajasthan infected maize. Wheat, rye and barley were susceptible to some of the tested isolates. The isolates from Rajasthan and Pakistan produced moderate to severe infection on at least one of these species. On rice, groundnut and sugar beet, only traces of infection by some isolates were detected, whereas no infection was observed on mustard and sunflower. Differences of susceptibility in Pennisetum spp. and Sorghum spp. were demonstrated. The variations in host specificity among isolates from peanut clump-infested areas may result from an adaptation of P. graminis populations to various biotopes. The implications of these results for the management of peanut clump disease are discussed. A comparison of the host ranges of isolates of P. graminis and P. betae from temperate areas demonstrated that distinct types of Polymyxa might be identified based on their relative ability to multiply on susceptible species. Nevertheless, overlapping in the host ranges among the different Polymyxa types, characterised by distinct ecological and genomic features, raises doubts about the host range as a classification criterion for the Polymyxa genus. Abbreviation: (I)PCV-(Indian) peanut clump virus.
The temperature requirements of three single cystosorus strains of Polymyxa sp. from India were studied at 15-18, 19-22, 23-26 and 27-30 C (night-day temperature), and compared with the temperature requirements of three strains of P. graminis from Belgium, Canada and France and two strains of P. betae from Belgium and Turkey. Sorghum was used as the host-plant for the Indian strains; the strains of P. graminis and P. betae from temperate areas were cultivated on barley and sugar beet, respectively. The cystosori germination and the development of plasmodia, zoosporangia and cystosori of Polymyxa sp. from India were optimal at 27-30 C. Infection progression was slower at 23-26 C than at 27-30 C. At 19-22 C, infection was insignificant. No infection occurred below 19 C. In contrast, the infection of barley with P. graminis strains from temperate areas was optimal at 15-18 C, but at 19-22 C the progression appeared inconsistent and infection stayed low. Above 22 C, infection was insignificant. P. betae strains showed consistent infection in the range of 15-18 C to 27-30 C. Plasmodia formation and cystosori detection of the Belgian strain were slightly advanced at 23-26 C compared to 19-22 C but clearly restrained at 27-30 C. Fungus development of the P. betae strain from Turkey was almost as high at 27-30 C as at the lower temperatures. These results strengthen the case for distinguishing between Polymyxa sp. from India and P. graminis or P. betae from temperate areas.
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