Identification of quantitative trait loci and comparison of selection methods for barley yellow dwarf tolerance in spring oats and winter wheat
Barley yellow dwarf (BYD) is one of the most destructive diseases of cereal crops worldwide. Barley yellow dwarf viruses (BYDVs) are responsible for BYD and affect many cereals including wheat and oats. Symptoms depend on cultivar and environment, but normally include stunted growth, leaf discoloration, inhibition of root formation and blasting of florets. Economic losses due to BYD are common in both wheat and oats due to reduced photosynthesis and inhibited roots. In the first study, the objective was to identify quantitative trait loci (QTL) for tolerance to BYD in the tolerant lines IL86-1156 and IL86-6404. A recombinant inbred line (RIL) population (Population 4) consisting of 115 lines, developed from a cross between IL86-1156 and the sensitive cultivar Clintland 64, was evaluated for BYD tolerance in the field at Urbana, IL in 2002, 2003, 2010 and 2011. A similar population (RIL population 5) of 177 oat RILs developed from a cross between IL86-6404 and the sensitive cultivar Clintland 64 was also evaluated for BYD tolerance in Urbana, IL over the same years. The populations had broad continuous distributions for BYD rating (0-9 scale). QTL for tolerance to BYD were identified on four chromosomes in RIL population 4 and seven chromosomes in RIL population 5. Two major QTL were observed on chromosome 3C and 19A in both populations. The QTL on chromosome 3C explained between 51.4% and 65.6% of the phenotypic variation while the QTL on chromosome 19A explained between 19% and 44%. Chromosomes with consensus QTL include 3C, 19A and 1C; however, 1C needs to be further investigated because it appears to be in a different location based on the population. Previous reports have identified large effect QTL for BYDV tolerance however; it is uncertain if they are in similar genomic regions. The results of this study indicate a few large effect regions are important for BYDV tolerance in IL86-1156 and IL86-6404. The markers that were found in association with these QTL can be utilized in breeding programs for parental selections. This can increase the efficiency of creating lines with BYDV tolerance by better selecting parents with complementary alleles at the important BYDV loci. In the second study, three different methods for evaluation of BYDV tolerance were compared for the amount of phenotypic variation they capture. In the first method, BYD rating, wheat and oat hills were rated on a 0 – 9 scale (inoculated vs control), with 0 being tolerant plants showing no symptoms and 9 being completely sensitive. This method is considered the standard procedure for evaluation of BYD. The second method, percent dwarfing, was a percentage calculated from the difference in height between the inoculated and controls hills. This method has been used in conjunction with BYD rating in wheat evaluations of BYD. The third method, percent biomass loss, was a measurement of the percentage calculated from the difference in total biomass between inoculated and control hills. In this study, 60 oat lines, as well as 118 wheat lines were evaluated using the three methods in Urbana, IL in 2011 and 2012. Genetic variances and standard deviations were used to determine the amount of variation in each method. Percent biomass loss exhibited the largest genetic standard deviations compared to that of BYD rating and percent dwarfing in both oats and wheat. Percent dwarfing had the next largest genetic standard deviation followed by BYD rating. Pearson correlations exhibited a similar trend throughout the oat and wheat tests. The strongest correlation was between percent dwarfing and percent biomass loss followed by biomass loss and BYD rating. The only exception was observed in the 5-State Test in wheat where percent biomass loss and BYD rating had the strongest correlation. The top and bottom lines were ranked with each method and examined for similarities with BYD rating. All the methods were able to rank the most sensitive lines very successfully. Percent biomass loss did a slightly better job ranking the top lines than percent dwarfing in similarity with BYD rating. To determine if a method should be recommended for use, the time required to collect data and the skill required to perform the tasks were taken into consideration. Percent biomass loss requires the most time and work for data collection but can be performed by less experienced workers in the breeding program. Percent dwarfing is much quicker than percent biomass loss and can also be performed by workers with less experience. BYD rating requires skill and experience to be performed correctly but can be done in a much quicker manner. The results of this study indicate that percent biomass loss does a better job capturing variation in BYDV infected plants but requires too much time to be used efficiently in a breeding program. The current methods of using BYD rating in oats and BYD rating in combination with percent dwarfing should continue to be used in breeding programs for tolerance to BYDVs.
spring oats, winter wheat, barley yellow dwarf virus (BYDV), Blue Yellow Dwarf (BYD), quantitative trait loci (QTL), selection methods, Single nucleotide polymorphism (SNP)
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign