Secrets revealed about Early blight and Pseudo-early blight CULTIVATION AND TECHNOLOGY Typically Early blight resembling symptoms of so-called mud mottling or eight-June disease. solani or any other fungi. Subsequently, a number of lesions were prepared in water agar in Petri dishes; if possible at least three leaves per sample and three lesions per leaf were used. It was then determined which organisms were clearly present in the lesions and/or colonised the agar. This showed that the presence of A. alternata was the same whether A. solani was present or not. If A. alternata has pathogenic potential, it can be statistically shown that this is negligible when compared with the pathogenic power of A. solani. Alternaria solani research A. solani was first found in one of the samples collected on 21 July. At the time, 31 samples with lesions that resembled an Early blight infection had already been sent, of which a total of 223 infections were prepared. No A. solani had been found in those. After 21 July, another 101 samples were sent in, of which 545 lesions were prepared. A. solani was found in 41 of those samples; in total it was found in 112 of the 219 prepared lesions. Consequently, 60 of these 101 samples did not have A. solani. During the entire study, 91 samples appeared to be free of A. solani. It is worth noting that another 31 samples were sent in during the period of 4 to 18 September, 29 of which contained A. solani. This means that the last two weeks of the FOLIAGE LESIONS Foliage lesions can have a variety of causes. Study has shown that foliage lesions often contain two organisms, namely the Alternaria alternata and the Cladosporium Cladosporioides fungi. The former is a mildly pathogenic organism. It is a parasite that focuses on weakened and dying tissue. The latter is a saprophyte that only settles on dead tissue. These organisms also occur in other foliage lesion diseases such as those caused by Phytophthora and Botrytis. A. solani is a pathogen that typically infects live tissue, it cannot colonise dead tissue. A. solani cannot compete with saprophytes on dead tissue. The real Early blight, caused by A. solani, in September 2009. study period resulted in the occurrence of more than 50 percent of the samples with A. solani. The results showed that A. solani occurred late in the 2009 season. Whether this was also the case in previous years is not known. The study also showed that over 50 percent of the samples with A. solani came in during the last two weeks, which underpins the late occurrence of Early blight. Finally, many of the symptoms of samples that were taken to be Early blight were, in fact, not those of A. solani; this was seen in 64 of the total of 112 samples sent in. This also means that crops widely sprayed against Early blight showed no A. solani infection. Yet the fact remains that many potato crops mature early with symptoms that resemble those of Early blight. Although A. alternata, like C. cladosporioides, is involved in Pseudoalternaria, it does not cause it. The final conclusion is that what was found in potato crops in the season of 2009 was not due to an Alternaria solani infection, but was connected to Pseudo-alternars and caused by ozone stress and boron deficiency. ● Dr L.J. Turkensteen, J. Spoelder M.Sc and Dr A. Mulder Potato World 2010 • number 4 23 Pagina 22
Pagina 24Interactieve etijdschrift, deze mailing of clubmagazine is levensecht online geplaatst met Online Touch en bied het online bladerbaar maken van digitale weekbladen.
Potatoworld 2010/4 Lees publicatie 18Home