Genotype By Irrigation Management Interactions in Elite Alfalfa Germplasm.

Rapidly diminishing surface and ground water resources threaten alfalfa production throughout much of the Great Plains and Western regions of the U.S.  Improving alfalfa productivity in such drought-prone environments is a critical breeding objective. The goals of this research were to: 1) assess the productivity of 24 elite alfalfa populations developed by conventional and DNA marker assisted breeding approaches under three flood irrigation management regimes near Las Cruces, NM, and 2) identify germplasms that are productive under highly variable soil moisture conditions.  Irrigation treatments consisted of 14-day (control) and 28-day (deficit) irrigation intervals throughout the growing season, and early irrigation termination which was managed similarly to the control during January to June, after which no irrigation was applied in July to December.  Forage was harvested monthly during late April through early November.  Average dry matter yields in the first production year (2015) were 20.4, 14.6, and 14.1 Mg ha^-1 for the control, early termination, and deficit irrigation treatments, respectively.  Leaf relative water content ranged from 83% under well-watered conditions to 63% in the deficit and irrigation termination treatments.  Significant yield differences were detected among populations in each study.  In the control and early irrigation termination treatments, populations performed comparably up through June (rank correlation, r_s=0.75).  When irrigation was terminated in July, little forage regrowth occurred.   Drought-related yield losses among populations in the control and deficit irrigation treatments ranged from 20 to 40%.  However, the irrigation treatment × variety interaction was not significant (P=0.20; r_s=0.40) for these two environments.  Populations were identified that performed well in all irrigation treatments, indicating that high performing germplasm with good yield stability may already be available to benefit western alfalfa growers.  Updated results from the second production year (2016) will be presented.