| The degeneration of potato is a typical case existed in the asexual reproduction plants. There are three major hypotheses, named ecological conditions induction, virus infection and natural aging, to explain the reasons and possible mechanisms of degeneration. Since the potato virus was discovered, it’s gradually accepted that the accumulation of infected virusesis the main factor leading to degeneration of potato. However,the concept of degeneration is still described and measured by appeared symptoms and yield reduction during continued cultivation without regeneration of planting materials. In order to understand the roles of virus disease and late blight on the degeneration of potatoes, 15 most popular cultivars of potatoes in China were planted in two consecutive years for observation of the effects of viruses and Phytophthora infestans(late blight) infection on yield and appeared symptoms of tested potato cultivars, by combining with the ELISA test for infected viruses and molecular marker detection of related resistance genes against viruses and late blight. The main results are as follows:1 The evaluation of late blight resistance in potato cultivarsWith the analysis of different methods for evaluating late blight resistance in the field trials, we recommended that, for the convenience to properly describe the resistant level of a potato cultivar, transforming AUDPC value into the qualitative resistance scale(1-5) with the aid of reference cultivar could be a better evaluation system on late blight resistance evaluationof potato than the others. Nevertheless, the difference of resistance to late blight between the plants and underground tubers should be noticed.2 Theeffect of late blight on the degeneration of potatoUnder the chemical control conditions, the average yield of tested cultivars in 2014 showed evidently and/or significantly higher than that in 2013. But the results reversed while no chemical control applied. The results reflected that late blightapparently and/or significantly affected the yield of the tested cultivars.3 Theeffect of viruses infection on the degeneration of potatoThe ELISA test showed that the virus infection rate of tested cultivars in 2014 was evidently higher than that in 2013, but the averaged yield in 2014 significantly surpassed that in 2013 for most tested cultivars. Integrated analyses of the source of seed-tubers, effect of aphids control, and epidemics of late blight during the experimental years, it’s evident that viruses infection diminished the yield of tested cultivars as well.4 Late blight and virus disease influence degradationComparing the yield per plant in 2014 and 2013, Nine of the ten yield varieties improved significantly in 2014,ELISA showed that potato virus infection rates in 2013 is significantly lower than the potato virus infection in 2014, late blight disease degree in 2014 was significantly lower than 2013, In this experiment, The harm degree caused by late blight is more higher than virus disease.4Molecular marker-based detection of R genes in tested potato cultivarsThe results of molecular marker-based detection of R genes revealed that the tested cultivars harbored known R genes against to late blight(R1、R2、R3a、R3b、Rpi-blb1) and potato viruses(Ns、PLRV.1、Rx1、Rychc), but quite different from each cultivars.The above results of two-year trials demonstrated that the effect of late blight on degeneration of potato(e.g. described as yield and diseased parameters of plants) was apparently and/or significantly over than that of infected viruses. |
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