I am looking for some information on the effect of doubled haploids on inbreeding depression in crop plants. Attaining homozygosity through several cycles of selfing leads to inbreeding depression in many crops. What is the inbreeding depression observed in plant made homozygous through anther/microspore culture? Haven't had much success in finding relevant literature through web search. Any help/guidance will be much appreciated.
As you say, inbreeding depression is caused by a lack of variation/diversity at each locus of a genome. Because anther/microspore culture creates uniformity "instantly" (i.e. without traditional propagation) the resulting plants are often very malformed, stunted, and lacking vigour - characteristics of inbreeding depression. Some plants will not survive this process at all. In my previous experience, certain species are more responsive to anther culture than others; such as Brassica oleracea which is fairly 'easy' to culture, but peas/legumes are not. In the initial DH procedure many plants are likely to be lost in the manner I have described; but some will propagate without any problems. When the progeny of these plants are again anther cultured, the survival rate tends to increase - you can think of it as a kind of selection pressure on the plants. The ones with genomes best suited for DH production will become more numerous in your DH population purely because they survive, and those lacking diversity will not do so well. I'm by no means an expert in this area, but just have a bit of experience with it. Please see the link attached to a book (Plant Breeding Reviews Vol. 25) which sums up the process quite nicely. I hope this helps :)
https://books.google.co.uk/books?hl=en&lr=&id=NQinOSRh9f0C&oi=fnd&pg=PA57&dq=doubled+haploid+inbreeding+depression&ots=Z46gLy3ho0&sig=SiF9tuTdV49VynYVWbit4pP5g9Y#v=onepage&q&f=false
Dear Hafiz, I agree with what Luke said. Tracing the nature of inbreeding depression in DH lines is indeed difficult because those plants hardly survive the variations. We have been involved with the development of some rice DH lines and have observed that, while it responded well with some Japonica rice lines, microspore culture exhibit a very low frequency with the Indica genotypes. This is mostly because of recalcitrant effect of the existing variations within a group of genotypes..
Thanks Luke and Raj. I was particularly looking for literature/research on differences (if any) in terms of manifestation of inbreeding depression between the two processes (conventional/DH). In terms of final outcome, the plants would show reduced growth etc. due to homozygosity attained at these particular (detrimental/lethal) loci (irrespective of the process employed). However, as has been alluded to in the discussion, the selection at the microspore level (as well as the numerous microspores subjected to such selection in vitro), may perhaps lead to the recovery of a higher number of surviving genoptypes (?).
I think this is correct. I don't know of any direct genomic comparisons between DH and inbred lines, other than to determine total homozygosity and the level of linkage drag that might occur through conventional inbreeding. After 5 generations of self pollination, most diploid species will be >99% homozygous at each loci, whereas (in theory) DH lines will be 100% homozygous at each loci from the start.
Earl Wernsman (NCSU) did some of the best pioneer work (quantitative genetic and molecular) here in tobacco. Look up some of his papers in Crop Science.
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