Ground Cover Supplement : GC Supplement - National variety trials
GROUND COVER NATIONAL VARIETY TRIALS 6 Disease ratings standardised ACROSS AUSTRALIA a standard system of disease rating is used in pulse variety evaluation, but this has not been the case for cereals or canola. With the establishment of NVT, and with varieties increasingly being sold across the country, the need for standard disease-rating systems for all crops has emerged. In 2008 standard colour-coded alpha systems were introduced for rating disease resistance in cereals, pulses and canola. "The development of a national standard system of ranking disease resistance marks a major step forward in variety testing," says Rohan Rainbow, the GRDC's crop protection manager. In the NVT database, and in reports sourced from NVT Online, only the alpha system will be used in order to avoid the confusion that could occur if the various regional numerical rating systems were recorded. Traffic light colours have also been added to alert growers to good (green), average (orange) and poor (red) levels of resistance (Table 1). Lines rated susceptible or very susceptible for any rust cannot be entered in NVT. However, due to resistance breakdown, commercial varieties that have been downgraded to susceptible (S) or very susceptible (VS) can still be found in NVT trials. The same colour-coded alpha system used for pulses and cereals has been introduced for canola, replacing the numerical system. Under the new nine- step alpha system resistant varieties will be rated 'R' and colour-coded green, while very susceptible varieties will be rated 'VS' and colour-coded red. However, there is an important difference in the interpretation of the 'R' resistance rating for canola. Ratings coordinator Dr Stephen Marcroft says it is important for growers to remember that an 'R' rating for canola does not mean it has immunity to blackleg. "The big difference between canola ratings and cereal ratings is what 'R' means," Dr Marcroft says. In cereals, 'R' equals immunity and means growers really do not have to do anything. But canola cultivars classified 'R' may not have sustained immunity to blackleg, so 'R' will mean the best resistance possible (Table 2). The NVT database uses one system of ranking disease resistance for all varieties, plus the 'traffic light' scale indicating poor (red), average (orange) and good (green) resistance By Rebecca Thyer ABOUT NVT AN 'R' RATING FOR CANOLA DOES NOT MEAN IT HAS IMMUNITY TO BLACKLEG TABLE 1 STANDARDISED CEREALS RESISTANCE RATINGS NOW USED IN ALL NVT CEREAL AND PULSE TRIALS Uniform rating Management option description For growers: What do I see? For growers: What do I do? Resistant (R) Disease may be found, but will be at such a level that no economic management is required, even in instances of high disease pressure. Trace levels of disease may be found. No economic management decisions required. Moderately Resistant (MR) Disease may be observed, but no economic management decisions will be required. Preventative sprays not necessary, but disease should be monitored. Management of seed quality may be required. The disease may be observed at very low levels. No economic management decisions required. Monitor crops for disease development. Moderately Susceptible (MS) In the presence of inoculum, and in seasons conducive to disease, the disease will be seen more readily when inspecting the crop. If the disease appears early in the season, then an economic management decision (preventative spray) may be appropriate. Later occurrence of the disease may not require any action. Management of seed quality will be required. In the presence of inoculum the disease will be seen more readily when inspecting the crop. Monitor crops for disease development. In the presence of inoculum and in seasons conducive to disease, an economic management decision may be appropriate (for example, preventative spray). Later occurrence of the disease may not require any action. Susceptible (S) The disease will be easily found in the crop. Management decisions will be required to reduce yield loss and it will most probably be economic to do so. Management of seed quality will be required. In the presence of inoculum the disease will often be easily found in the crop. Management decisions will be required to reduce yield loss and it will most probably be economic to do so. Very Susceptible (VS) Do not grow this variety if the disease in question is a regular occurrence or risk. The variety in question can be a complete loss if sown and no disease management is applied. The disease will be obser ved readily in the crop. If this variety is to be grown in areas at risk of disease development, additional management strategies are essential.
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