Development of guayule mapping population

Guayule is a source of natural rubber. The crop can perform well in marginal soils/climates as it is extremely drought tolerant as it evolved as a shrub in the deserts of Arizona and Mexico. It can yield between 10 and 20 ton of dry matter per year with 10 % rubber and 10 % resins, and the remainder is lignocellulose (9-18 ton/ha). It can be grown in many areas of Europe as shown previously in the EU-project EU-PEARLS. Genetic improvement is hampered by lack of well characterised populations. Especially, populations segregating for major traits that can be used for mapping quantitative trait loci for yield, rubber and resin content and lignin content (related to ease of biorefinery processing) are yet to be developed.

This project will use open pollinated offspring of several guayule lines differing highly in productivity, rubber content, resin content and structure of the stem cell wall material.

Only a small fraction of such open pollinated offspring is the result of crosses as the lines have a high fraction of apomictic reproduction. In order to efficienty select offspring resulting from  crosses, a large number of offspring needs to be analysed using molecular markers to the real F1-hybrid offspring. This project will use already available RNAseq data from 8 lines of guayule to develop PCR-markers that can be used to identify offspring from crosses. PCR-markers that are unique for a certain parent will be tested in the offspring harvested on the other parent lines (the motherline). As the PCR marker is unique, large groups of offspring can first be tested for the occurrence of hybrid offspring using pooling strategies (e.g. 2D pooling) to reduce the number of PCRs to be carried out. From each maternal line about 1,000 offspring will be tested (in total about 5,000 to 10,000) until sufficient hybrid offspring have been identified. Seed will be harvested of those offspring that arose by sexual reproduction. The offspring of such hybrids will consist of F2-seed and of apomictic offspring. Both types of offspring can be used for later genetic analysis that will yield a genetic map of guayule and identification of trait-DNA markers links.