Development of Dual Use Maize Cultivars | Corn as Food and Stover for Biogas Production

Arable land resources for the production of food, feed and energy are limited. The increasing use of maize for bioenergy production is critically discussed in public. By developing dual use maize varieties combining the use of grains for feeding animals with the use of leaves and stem as substrate for biogas production, the conflict between food/feed and energy production will be mitigated. With the development of dual use maize cultivars an interesting alternative has been found to increase the economic and environmental value of maize in Germany. Present cultivars cannot be used as dual use maize because of their low water content and sugar content in the stover. Dual use maize varieties have to combine characteristics different from grain maize, silage maize or energy maize, like: 1. High grain yield (nearly as high as grain maize) 2. High yield of stover (stem and leaves) with a: a. High water content of stover b. High sugar content of stover 3. Stay-green behavior indicating long photosynthetic activity even when the grains are mature The combination of different characteristics for dual use maize cultivars is asking to investigate breeding methods for dual use maize cultivars. The switch from grain maize or energy maize production to grain maize and energy maize production is only possible if the requirments for an efficient development are given. Eventhough the genetic background of sugar content in the stover and stay-green behavior is of great interest while investigating in breeding methods. To breed for dual use maize cultivars 178 testcrosses (89 Dent line x Flint tester and 89 Flint lines x Dent tester), coming from the actual breeding material of KWS SAAT SE have been cultivated in 2014 at three different locations in two different performance tests (silage maize and dual use maize) in Southern Germany. In 2015, 88 factorial crosses, received by the best lines have been tested at three different locations in Southern Germany for their performance as silage maize and dual use maize. The ‘stay-green’ behavior and the sugar content in the stover of the Dent and Flint testcrosses was measured in observations tests at two locations (Einbeck and Göttingen) over three years. Both traits have been measured in the factorial crosses as well for two years at the same two locations (Einbeck and Göttingen). The selection of the best lines was based on the their ‘stay-green behavior’, grain dry matter yield, total dry matter yield, water content of the stover and sugar content of the stover, compared to the grain dry matter content and total dry matter content. Seven Dent and thirteen Flint lines have been selected High grain dry matter yield and high yield of stover are not easy to combine, but it is found that the correlation is low between the two traits. The sugar content of the stover was measured with the BRIX method, showing the sucrose content of the sample in % BRIX. The stay-green behavior was measured with the SPAD-method, which is highly correlated with the chlorophyll content. Both traits have been showing a high heritability but a low correlation to each other. Genotypes are found that are showing stay-green behavior during dual use maize harvest, in combination with a high grain dry matter yield and stover dry matter yield. The water content and the sugar content of the stover are high, to garantuee a stable biogas production. On the other hand, genotypes showing a high total dry matter yield during silage maize harvest, are not necessarily the best preforming genotypes in dual use maize harvest. Therefore indirect selection for dual use maize by selection during silage maize harvest is not possible. The response to this indirect selection is very low, and therefore the complicated and time consuming dual use maize harvest is necessary to conduct the best results. After finishing the second experimental year one promising genotype has been submitted by KWS SAAT SE to official variety tests. These cultivar can be used as grain maize with additional use of stover for biogas production. In a second part of the study, genome-wide association mapping was conducted for 81 Dent lines and 84 Flint lines. The lines were genotyped with 8917 single nucleotide polymorphisms (SNPs) using the 12K KWS Illumina Chip. The population structure was analyzed with a principal coordinate analysis. The first ten principal coordinates have been used to correct for population structure. The Dent population is showing a high familial relatedness, while the population structure of the Flint population indicating two subpopulations. Genome-wide association mapping was done with the general linear model, corrected for population structure and the mixed linear model, correcting for population structure and familial relatedness in the program TASSEL Version 5.0. The general linear model is showing several statistically significant associations between marker allels and variation in sugar content and chlorophyll content, which are supported by the mixed linear model. For the sugar content of the stover (BRIX) the Dent population is showing significant associations on chromosome 2 and chromosome 4. The Flint population is showing associations for the sugar content on chromosome 1. ‘Stay-green’ behavior was measured two times, eight weeks before harvest and one week before harvest. For the first measurement (eight weeks before harvest) associations are found on chromosome 2 and chromosome 3 for the Dent lines, while the Flint lines are showing no significant associations. For the second measurement (one week before harvest) both populations are showing associations on chromosome 2. The Dent lines are showing as well on chromosome 8 associations, while the Flint lines are having associations on chromosome 9 as well. Furthermore it is shown that the findings are supported by already done studies, finding QTLs for stay-green behavior and sugar content in the stover. Identifying methods of breeding for dual use maize have been the main objective. Switching from grain maize or energy maize production to grain maize and energy maize production is a great option, because of the high environmental and economic value for farmers. To become a meaningful alternative to mitigate the conflict between food and energy production more research should be investigated in better harvest systems and silaging of maize stover in biogas plants, by analyzing the methane yield of the stover. Usage of additional trace elements for stable biogas production and editing other co-substrates has to be analyzed as well. The genetic background of the traits sugar content of the stover and stay-green behavior should be studied further, with developing specific markers and QTL mapping to get a powerful breeding tool.