Screening for SCN resistance and field evaluation of soybean recombinant Inbred lines
Niyikiza, D., G. Dickey, J. H. Rice, T. Burch-Smith, P. Arelli, C. E. Sams, T. Gill, T. Hewezi, and V. R. Pantalone.  2018.  Molecular & Celluar Biology of the Soybean.

Soybean Cyst Nematode (SCN) is the most damaging pathogen in the US and in the world. Annual yield losses due to SCN are estimated to cost over $1.2 billion in the US. Breeding for resistance has been the main strategy to control SCN and maintain yields. However, the sole use of a single source of resistance from PI 88788 caused a shift in virulence of SCN populations and the latter became adapted, breaking the resistance of most of the available commercial cultivars. In addition, there have been reports associating SCN resistance to a considerable yield drag especially in sites with no or few SCN inoculum. In this context, there is a need to continuously develop new lines with multiple sources of resistance to SCN. We evaluated 115, F5 derived recombinant inbred lines (RILs), resulting from a cross between TN09-029 and NCC05-1168. The population was segregating for SCN and resistance to other diseases, yield as well as other agronomic and seed quality traits. The lines were evaluated over two years in 5 environments across Tennessee, each with two replications in a completely randomized block design. These lines were also screened for resistance to SCN race 2 (HG with each line in 5 replications in greenhouse bioassays. Female Indexes (FI) were calculated based on susceptible standards (Hutcheson or 5601T). Lines with FI<10% were recorded resistant and FI>10% susceptible. Differences were registered in yield (P<0.001) and other traits. The RIL top yielders (SCNepi-134= 4154.76 kg ha-1, SCNepi-043=3940.63 kg ha-1) were found in the same group as the check (Ellis = 4057 kg ha-1). No significant differences were found between the mean seed yield of the resistant lines (3,369.5 kg ha-1) and the susceptible lines (3,411.2 kg ha-1). These results suggest that resistance to SCN race 2 does not necessarily impede yield