This study aims at evaluating known and new sorghum genotypes for agronomic traits, nutritional and other factors of importance for yield and it’s used for bioenergy under contrasting agro-climatic conditions: Denmark and Nigeria. Two diverse collections of Sorghum bicolor L. (Moench) accessions were used, one adapted to the tropical climate in Nigeria and the other developed for the
temperate climate in the Netherlands. It is anticipated that sorghum can be breed for cool climate growth like Denmark similar to what has been achieved with maize breeding over the last 30 years. Sweet sorghum as a bioenergy crop has gained interest because it accumulates sugar in the stem while still producing seeds and could be an attractive alternative to maize and in crop rotation. For the production of sorghum in Nigeria the parasitic weed Striga hermonthica is a major challenge.
The present PhD study three field trials was conducted in 2014 and 2015 with sorghum accessions obtained from ICRISAT and a Dutch breeding population to evaluate: (1) the reactions to the parasitic weed Striga hermonthica in Bida, Niger State, Nigeria in order to identify new tolerance to the pest; evaluate. (2) Interaction with contrasting agro-climatic conditions in Denmark and Nigeria; and (3) determination of stem sugar and evaluation of the potential for bioenergy under these two growth conditions.
In the first study of 91 sweet sorghum accessions large variation in the resistance and susceptibility to Striga hermonthica was found even all sorghum genotype had very similar and high plant vigour. The overall resistance in the ICRISAT accessions was found to be 33 %, whereas for the Dutch sorghum accession resistance was found to be 21 % across the two years of evaluation. Based on the crop yield and the severity of infection scores, seven genotypes of ICRISAT accessions were identified to be high yielding with high to medium resistance while four Dutch genotypes were found to be resistant and high yielding. In total eleven promising sorghum genotypes identified to be resistant to Striga, while thirteen genotypes appeared to be tolerant. One of the Dutch genotypes showed high yield and good resistance and with a potential in tropical climate. This is the first time the Dutch material was tested in tropical climate and showed that even if it have never been tested for reaction to Striga, it can provide genetic resource for resistance in a breeding program aiming at Nigeria.
The analysis using AMMI and GGE biplot showed the performance of the 43 genotypes to be location specific. Eight of the ICRISAT accessions gave Brix values above 14% when grown in Denmark, which means that high stem sugar concentrations can be achieved in cool climate. Only one of the Dutch accessions had Brix value above 10% which may reflect that adaptation has been a major selection criteria rather than bioenergy relevant traits. The level of variations of the various agronomic traits expresses the true genetic potentials of the evaluated accessions.
Proximate analysis of the seeds revealed no significant differences in nutritional composition. Only few accessions showed reasonable values in sugar, fat and calcium content.
In conclusion the study show that in particular Dutch breeding material has strong potential for adapting to Danish agro-climatic conditions and also to bring in new Striga tolerance in breeding for tropical climate. The ICRISAT collection is more advanced regarding sugar concentration in the fields in Denmark.