Plant improvement to increase the water‐use efficiency of affalfa (Medicago sativa L.) has been limited. This study compared leaf color variants (pale and dark) to evaluate the effect of alfalfa leaf chlorophyll on water relations and yield of alfalfa. Leaf color populations were selected from ‘Ladak 65’ and visually selected sub‐populations evaluated under controlled‐environment and field conditions. Seven moisture regimes were established in controlled environment studies in which a commercial root medium with high water‐holding capacity was used. The field study was at Laramie, WY, on a Wyocolo soil (fine, loamy, mixed Borollic Haplargid) and consisted of irrigated and nonirrigated treatments. Traits measured for the two populations included leaf chlorophyll (Chl), leaf photo‐synthesis (as CO2 exchange rate: CER), transpiration (T), stem pressure potential (ψw), water‐use efficiency (WUE), leaf area, forage yield. Controlled. environment conditions produced pale plants that contained 15% less total Chl than dark‐leaved variants. The Chl concentration of pale variants was equal between the moisture extremes, while the dark variants decreased 20% for the low‐moisture (compared with high moisture) regime in the controlled environment. The WUE in the controlled environment of pale and dark leaf types averaged 1.47 and 1.22 g dry forage kg−1 water, respectively. This difference in WUE was attributed mostly to the greater growth of pale leaf types. The CER and CER/T ratio of the dark leaf types were more sensitive to moisture stress than the pale types. In the 2‐yr field study, the pale leaf types had a 22% lower CER than the dark leaf types across moisture regimes and 19% lower T under the irrigated regime. Even though leaf photosynthesis was lower for the pale leaf types, the forage yield was 25% higher under the irrigated regime.

Winter injury of the winter pea (Pisum sativum subsp. arvense (L.) Poir) crop of northern Idaho causes severe losses. The development of cultivars with higher levels of winterhardiness would increase both the seed yield and area of adaptation of this crop. To evaluate techniques for determining winterhardiness in peas, 14 genotypes of winter‐hardy peas, and six genotypes of spring peas (P. sativum L.), were screened in the field and laboratory. Trials were planted on three dates at Moscow, Idaho, and a single date at Bozeman, Mont., during the fall of 1976 and 1977. Seedlings were counted in both the fall and spring to determine the percent survival. At all planting dates and locations, the spring pea cultivars failed to survive the winter, indicating that spring types can be eliminated from segregating populations by fall planting. Three lines, ‘Romack’, ID 89‐1, and C8‐M‐23, appeared to be intermediate in winterhardiness and could be used as controls in future trials. Screening at −9 C in a programmable freezer eliminated all spring cultivars and produced differential survival among the winter‐hardy lines. Correlation coefficients between percent survival of the 13 winter‐hardy lines in the eight field environments and three test temperatures indicated that screening in the laboratory at −9 C successfully identified those lines with intermediate levels of winterhardiness. Fourteen lines of the P. sativum and four lines of the P. arvense USDA plant introduction collection had usable levels of winterhardiness in field trials at Moscow.

Legume seedlings from seed of different sizes compete with one another in pure seedings, usually to the detriment of smaller seedlings. We seeded variable rates of sized‐seed at Bozeman, Mont., to determine if less competition would permit lowering the seeding rate of alfalfa. We screened alfalfa (Medicago sativa L.) seed to small, medium, and large sizes weighing 160, 210, and 256 mg/100 seed respectively, and also made up a composite of the three sizes. We planted seed of each size at seeding rates of 1.1, 2.2, 4.5, and 9.0 kg/ha into a Bozeman silt loam (Agric‐Pachic Cryoboroll) soil in the field and measured seedling emergence and survival and yield in the year following seeding. Number of seedlings that emerged and number of plants that survived the second year were closely related to seeding rate. Percentage of planted seeds, resulting in mature plants from two separate plantings, decreased with increased seeding rate due to more intraplant competition. More seedlings emerged from small seed, or from the seed composite of all sized‐seeds, than from medium or large seeds. Seed size did not affect yield in the year of seeding or the year following. A seeding rate as low as 1.1 kg/ha at one location and 2.2 kg/ha at a second location gave maximum yield in the year following seeding. Our data showed no advantage of sizing seed. Seedling density was as good or better with small or composited seed as with large seed at the same seeding rate.

The development of cultivars with the ability to germinate under high salt stress would be useful in the reclamation of saline soils. One of the major problems has been the development of uniform, repeatable methods for selecting for the ability to germinate under salt stress conditions. Our objectives were to determine if agar could be successfully used as a saline medium to rapidly screen large numbers of alfalfa (Medicago sativa L.) seeds for ability to germinate under salt stress, and if progress through selection could be made for this trait. Seeds from 15 different alfalfa cultivars were germinated on agar containing varying concentrations of NaCI. Significant differences among the cultivars were observed for ability to germinate under salt stress. Selection within 'Ladak 65' at 1.75% NaCI in the agar medium resulted in a 3.75 fold increase in germination at that salt concentration. Selection within Ladak 65 using NaCI on blotters did not improve germination on saline agar.

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