Semester of Graduation

Fall 2018

Degree

Master of Science (MS)

Department

Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Mosaic is a viral disease of sugarcane caused primarily by Sorghum mosaic virus (SrMV) in Louisiana. Low mosaic incidence has resulted from successful breeding for resistance. However, mosaic was detected in breeding program experimental clones and a new cultivar, HoCP 09-804.Therefore, multiple research approaches were undertaken to assess the current status of mosaic in Louisiana sugarcane and prevent it from re-emerging as an important problem. Field surveys conducted during 2016-2018 of breeding program yield trials and experimental clone seed-cane increases determined disease incidence and distribution. Mosaic was detected in three of five sugarcane production areas and incidence ranged from 0 to 10% in HoCP 09-804. Symptomatic and asymptomatic leaves were tested for SrMV with reverse transcription polymerase chain reaction (RT-PCR). All symptomatic leaves tested positive for SrMV confirming it is the current causal virus species. A low percentage of asymptomatic leaves (0.3%) tested positive for SrMV. Runs analysis detected aggregation of infected plants in rows of surveyed fields. The geographic and within field distribution suggested the source of disease was infected seed-cane. Subsequent surveys of the same locations detected incidence increases and decreases in first ratoon, but incidence decreased for all in second ratoon. The results suggest high rates of disease increase due to aphid transmission are not occurring under current conditions. Recovery from mosaic was evaluated as the emergence of asymptomatic plants from symptomatic stalks. L 10-147 had a higher frequency of recovery (9.4-18.9%) than HoCP 09-804 (0.9-2.3%) across two experiments. RT-PCR failed to detect SrMV in 83% of HoCP 09-804 and 97% of L 10-147 of recovered plant samples. Comparison of asymptomatic and symptomatic stalk plantings found mosaic reduced yield in HoCP 09-804 but not L 10-147. Sources of susceptibility were evaluated in the basic and commercial parent populations by mechanical inoculations. Mosaic susceptible parents were identified within both populations. The level of susceptibility within the basic parent population was low indicating it will continue to be a resource for continued introgression of mosaic resistance. The results will allow the elimination of sources of susceptibility and informed crossing to continue successful management of mosaic with host plant resistance.

Date

10-24-2018

Committee Chair

Hoy, Jeffrey

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