Yield Loss in Cereals, Caused by Fusarium culmorum and F. pseudograminearum, Is Related to Fungal DNA in Soil Prior to Planting, Rainfall, and Cereal Type.

In southeastern Australia, Fusarium crown rot, caused by Fusarium culmorum or F. pseudograminearum, is an increasingly important disease of cereals. Because in-crop control options are limited, it is important for growers to know prior to planting which fields are at risk of yield loss from crown rot. Understanding the relationships between crown rot inoculum and yield loss would assist in assessing the risk of yield loss from crown rot in fields prior to planting. Thirty-five data sets from crown rot management experiments conducted in the states of South Australia and Victoria during the years 2005 to 2010 were examined. Relationships between Fusarium spp. DNA concentrations (inoculum) in soil samples taken prior to planting and disease development and grain yield were evaluated in seasons with contrasting seasonal rainfall. F. culmorum and F. pseudograminearum DNA concentrations in soil prior to planting were found to be positively related to crown rot expression (stem browning and whiteheads) and negatively related to grain yield of durum wheat, bread wheat, and barley. Losses from crown rot were greatest when rainfall during September and October (crop maturation) was below the long-term average. Losses from crown rot were greater in durum wheat than bread wheat and least in barley. Yield losses from F. pseudograminearum were similar to yield losses from F. culmorum. Yield loss patterns were consistent across experiments and between states; therefore, it is reasonable to expect that similar relationships will occur over broad geographic areas. This suggests that quantitative polymerase chain reaction technology and soil sampling could be powerful tools for assessing crown rot inoculum concentrations prior to planting and predicting the risk of yield loss from crown rot wherever this disease is an issue.

Effect of Field Crops on Population Densities of Pratylenchus neglectus and P. thornei in Southeastern Australia; Part 1: P. neglectus.

Eighty-one cultivars from 12 field crop species were assessed for suitability as hosts to the root lesion nematode, Pratylenchus neglectus, in two field trials. Host status was assessed on the basis of either final P. neglectus densities in soil or multiplication rate under different crops. Both techniques gave consistent results for crop and cultivar ranking, and it was therefore concluded that, in these trials, final population density could be used for screening cultivars for resistance to P. neglectus. Differences were observed among crops and cultivars for host suitability to P. neglectus. Chickpea, wheat, and canola were good hosts, while barley, oat, durum wheat, medic, and vetch were moderate hosts. Field pea, faba bean, and triticale were poor hosts. A range in host suitability was observed for wheat, barley, and oat cultivars.

Effect of Field Crops on Density of Pratylenchus in SouthEastern Australia; Part 2: P. thornei.

The effect of 93 field crop and pasture cultivars on the end-of-season population densities of Pratylenchus thornei in soil was determined in the field in southeastern Australia. Wheat and barley cultivars had different effects on the population densities of P. thornei. Most commercial wheat cultivars that are grown in southeastern Australia were susceptible, while the barley cultivars were resistant or moderately resistant. Lentil, field pea, fenugreek, linseed, and medic were found to be resistant to P. thornei, while faba bean and canola were moderately resistant and narbon bean, subterranean clover, and vetch were susceptible. This study will enable growers to select rotational crops to reduce the population densities of these nematodes and therefore minimize the yield loss they cause.