Pearl Millet Grain Yield Loss from Rust Infection

Pearl millet [Pennisetum gluucum (L.) R. Br.] has potential as a feed grain crop in the USA, but acceptance by growers will depend in part on its yield stability. The effects of rust, caused by Pucciniu substriuiu var. indica, on grain yield of the pearl millet hybrid ‘Tift 23DA₁,E × Tift 8677’ were evaluated at Tifton, GA from 1992 to 1994. Treatments imposed to vary disease severities in 1992 consisted of inoculation, control, and three fungicide applications (chlorothalonil[2,4,5,6-tetra-chloro-l,3-benzenedicarbonitrile], Bravo 720 @ 0.46 oz/gal [3.6 ml/L]). Treatments in 1993 consisted of a control and one or three fungicide applications. Treatments in 1994 were control, two, four, or seven fungicide applications. Early planting in 1992 resulted in crop maturation during early development of the rust epidemic. Mean final disease severities ranged from 0 to 33%. No differences among treatments for yield or 500 grain weight were detected. Late planting in 1993 was more conducive to rust development, and mean final severities ranged from 36 to 96%. Grain yield and 500 grain weight of the control were reduced by 76% and 41%, respectively, of those yield components measured from plots with three fungicide applications. Protein concentration of grain averaged 10.8% (108 g/kg) and did not differ among treatments in 1993. Rust was severe in 1994 as a result of late planting coupled with frequent rain, and averaged 92% severity in plots receiving seven fungicide applications. Grain protein averaged 23.3% (233 g/kg) in 1994, and increased with rust severity. Indirect yield losses from lodging occurred in 1993 and 1994 when final rust severity exceeded 90%. Regression equations suggest that yield losses occur when disease severity exceeds 50%. Until resistant hybrids are available, grain losses may be avoided by planting the crop by early June. Research QuestionPearl millet is commonly grown as a forage crop in the southeastern USA, but grain-producing hybrids have potential value in rotation systems. The value of grain pearl millet depends, in part, on its yield stability, which may be affected by diseases. The objective of this research was to evaluate the losses of pearl millet grain yield caused by rust infection. Literature SummaryRust is the most important disease of pearl millet in the Southeastern USA. Low levels of infection reduce digestible dry matter yield of forage. Although pearl millet is grown as a grain crop in many areas of the world, little information is available concerning losses of grain yield from diseases. Study DescriptionA susceptible experimental hybrid was evaluated for 3 yr at Tifton, GA. Different rust severities were imposed on the plots by differential inoculation or application of fungicide. Percentage lodging and rust severity were determined prior to harvest. Protein concentration of grain was analyzed. Applied QuestionsDoes rust infection affect grain yield and protein concentration of grain? Rust infection reduced grain yield and grain weight in 1993 and 1994. Protein concentration increased only in 1994 when rust infection was severe and grain losses were greatest. Lodging increased as rust infection increased. There appeared to be little or no loss of grain yield or grain weight until rust severity approached 50% at harvest, but losses occurred rapidly after that level of severity. The loss of pearl millet grain yield to rust infection differs considerably from losses of digestible dry matter yield of forage pearl millet. Grain pearl millet may be able to withstand greater rust severities than forage pearl millet without yield losses. Can grain losses be managed by date of planting? Number of days with rain 45 d prior to harvest were similar for the 1992 and 1994 experiments, but rust severities differed. The later planting date in 1994 resulted in crop maturation during development of the local rust epidemic. Pearl millet was planted in early July 1992 and the crop matured prior to the onset of severe rust infection, however, rust severity approached the level where yield losses were likely to occur. Planting by early- to mid-June would increase the probability that grain fill would be complete prior to the onset of rust epidemics. Fig. 1Loss of pearl millet grain yield in response to severity of rust infection at Tifton, GA, from 1992 to 1994.