2009 Annual Report
1a.Objectives (from AD-416)
The long-term objective of this project is to reduce the impact of diseases on the productivity of the domestic sugarcane (Saccharum hybrids) industry by providing assistance to sugarcane breeders in identifying parental clones with resistance, improving the efficiency of selection for disease resistance traits, and providing the industry the information needed to guard against more virulent strain shifts and/or new pathogens. Our primary objectives will be to identify and develop germplasm with resistance to the major diseases affecting sugarcane, to identify the genetic variability among endemic pathogen populations, and to monitor the Louisiana sugarcane industry for the emergence of new pathogens. Disease resistant germplasm will be sought from among different taxa of Saccharum and related genera. Molecular markers that are linked to genes for disease resistance will be identified. Molecular approaches will be used to enhance the studies of host and pathogen genetics.
1b.Approach (from AD-416)
To identify and develop germplasm with resistance to the major diseases affecting sugarcane in the United States, highly domesticated and wild clones of sugarcane and near relatives will be evaluated for resistance to the major sugarcane diseases following either natural and infections or artificial inoculation. To identify molecular markers that are linked to genes for disease resistance, polymerase chain reaction (PCR) based methods such as AFLP, SSR, or TRAP will be used to identify genetic markers closely linked to the resistance genes. Priority will be given to finding markers for smut, then ratoon stunting disease (RSD) and mosaic. Genotypic and phenotypic expressions of variability within populations of pathogens will be used to identify the genetic variability among pathogen populations and determine the distribution of races, strains, or other biotypes. The domestic sugarcane industry will be monitored for the introduction of exotic pathogens.
Project receives support from the American Sugar Cane League (6410-21000-014-04T) through a Trust Fund Cooperative Agreement, ”Improving Sugarcane Production Efficiency", as well as the in-house project 6410-21000-014-00D, "Genetic Improvement of Sugarcane by Conventional and Molecular Approaches". Additional details of research can be found in the reports of the subordinate and parent projects.
Greenhouse disease trials of 86 wild relatives of sugarcane and progeny from crosses involving the wild sugarcane relatives were continued. The results of inoculating the wild relatives with the ratoon stunting disease (RSD) bacterium that causes severe symptoms in the regrowth (ratoon) of a plant following cutting at the base, and the mosaic viruses were evaluated in early FY 2009. The wild relatives were also inoculated with the leaf scald and smut pathogens and evaluated in FY 2009. Near commercial-type varieties (387) that are progeny of wild relatives and commercial varieties were inoculated in the field with the RSD bacterium and evaluated for susceptibility.
Varieties (83) for possible commercial release in the next five years were screened by artificial inoculation for susceptibility to smut and leaf scald. Candidate varieties (738) that could be released in 8 years were screened by artificial inoculation for susceptibility to RSD. Candidate varieties in other ARS breeding trials and nurseries were evaluated for susceptibility to natural infection by the pathogens causing mosaic, rust, smut and leaf scald diseases. Pathology recommendations were made at variety advancement and variety release meetings.
Genetic analysis of DNA was completed using 66 SSR markers for the 286 progeny from the selfing of the sugarcane variety, LCP 85-384. Of the 286 progeny, 277 were verified as being true selfs. The progeny were multiplied and screened in greenhouse and field tests for susceptibility to RSD, mosaic, smut, and rust. Only two out of 277 were susceptible to smut by inoculated test in the greenhouse; however, approximately 5% of the progeny were susceptible to natural inoculation in the field. Susceptibility to RSD ranged from resistant to highly susceptible. The 25 most susceptible and the 25 most resistant were identified for future genetic analysis. Natural infection by brown rust was recorded.
Since the discovery of orange rust on sugarcane in Florida in 2007, its possible spread into the Louisiana sugarcane production area has been monitored. No evidence for the presence of orange rust of sugarcane in Louisiana was found in 2007 or 2008. Rust spores collected from pustules on plants of five commercial varieties located on farms and from pustules on approximately 10 experimental varieties being tested at multiple locations were identified as spores of brown rust which has been present in Louisiana since 1981. Monitoring of the Louisiana sugarcane industry continues.
Response of Louisiana's Leading Sugarcane Varieties to Ratoon Stunting Disease (RSD). The popularity of the sugarcane variety LCP 85-384 increased rapidly following its release in 1993 until it occupied 91% of the Louisiana sugarcane production area in 2004; however, because of concerns over declining yield of the variety, growers are replacing it with newer varieties. Four field experiments were conducted beginning in 2000 to determine the susceptibility of the seven varieties released since 1999 to RSD caused by a bacterium that lives in the water vessels of the sugarcane stalk. In two of the newer varieties, L 99-226 and L 99-233, a high percentage (>50%) of the water vessels were infected with the RSD bacterium and yield loss was detected in infected plants of both varieties. In two other varieties, HoCP 91-555 and HoCP 00-950, a moderate number of water vessels (25-50%) was infected, but yield loss was only observed in one, HoCP 91-555. In the other three varieties, Ho 95-988, HoCP 96-540, and L 97-128, a low percentage of water vessels were infected and no yield loss was detected. Although yield loss was not observed in plants with low levels of bacterial infection, growers should continue to plant stalks of cane that are free of the bacterium to prevent spread to more susceptible varieties and to prevent the compounding of effects that may occur if the infected crop is exposed to additional biological or environmental stresses.
Yield Loss in Four Louisiana Sugarcane Varieties Caused by Sugarcane Yellow Leaf Virus Infection. Sugarcane yellow leaf virus (SCYLV) causes yellow leaf disease of sugarcane. In Louisiana, the obvious visual symptoms of yellow leaf are rarely observed because during the later part of the growing season when the symptoms would typically be produced, they are masked by the effects of chemical ripeners, frosts, or freezes. The purpose of this study was to compare the cane and sugar yields of SCYLV-infected and non-infected plants of four varieties (LCP 85-384, Ho 95-988, HoCP 96-540, and L 97-128) that currently occupy over 90% of the sugarcane acreage in Louisiana. In a series of experiments, cane and sucrose yields of SCYLV-infected plants were reduced in LCP 85-384, HoCP 96-540, and L 97-128, while no yield reduction was observed in Ho 95-988. No visual symptoms of yellow leaf were observed among the plants of these experiments. The results of this study indicate that SCYLV-infection can result in loss of cane and sugar yields among these important varieties even when disease symptoms are not produced. However, the impact of the disease is less than that reported in other states and countries. To minimize the potential for yield loss from SCYLV infection, growers should plant seed cane free of the virus.
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Grisham, M.P., Eggleston, G., Hoy, J.W., Viator, R.P. 2009. The effect of sugarcane yellow leaf virus infection on yield of sugarcane in Louisiana. Sugar Cane International. 27(3):92-95.