Last week the Early Bird Decision meetings were held in Western Kentucky to assist growers with their grain seed purchases for 2008.

There were a few questions regarding the superior yields with some of the Bt hybrids and stacks, particularly those with the RW genes. Results from some county strip trial demonstrations had indicated that these hybrids out yielded their ‘isolines’ without the Bt RW gene. This is not unusual at all, except that in these instances, there was no rootworm pressure in these fields. So why would we expect a yield bump when studying these comparisons?

One consideration that I have is how similar are these ‘isolines’ with and without Bt genes. It has been observed that in some instances the isolines can differ in other agronomic characteristics other than just insect resistance. For example, one county agent noted that two isolines differed in relative maturity by three days. This suggests to me that the isolines are differing in some of their background genetics apart from the presence or absence of the Bt RW traits. The breeding methods used to add a gene into a hybrid involves backcrossing an experimental line with the gene of interest into one or both of the inbred parents used to make a hybrid. The number of times it is backcrossed with the inbred parents will determine the degree to which it is genetically similar to the parent. For example, if 4 backcrosses are used to incorporate the gene into an inbred, then the modified inbred would be (1-0.54) *100% or 93.75% similar to the original inbred. With six backcrosses that would become (1-0.54) *100% or 98.44% similar. What that means is that there may be differences in the background genetics beside the Bt RW gene. The differences in yields observed in some of these trials might not be due to the presence or absence of the Bt triats, rather they may be due to other agronomic differences, even among isolines. Keep in mind that the individual traits will not necessarily make a hybrid yield better, the entire genetic package is critical to final yield potential and yield is still a dominate factor when selecting hybrids.

[editors note – this is one reason why the doubled-haploid process from GLH is far better than competitors using backcrossing. The doubled-haploid process makes an identical copy or clone of the original hybrid with the new trait in it, thus 100% pure, not 93-98% pure. For more information on doubled-haploids, click here.]

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