Low profit potential as well as environmental residue and toxicology concerns make it difficult for chemical companies to develop and register herbicides for forage crops. Selection of forages with tolerance to currently labeled herbicides may be an alternative. The objective of this research was to develop a 2,4‐D [(2,4‐di‐chlorophenoxy) acetic acid] tolerant red clover (Trifolium pratense L.) population, using recurrent half‐sib family selection. A 20 000 plant base population of equal parts of ‘Nolins’, ‘Kenstar’, and a Florida population (QC5) was sprayed with 1.12 kg ha−1 2,4‐D and 63 individuals were selected and intercrossed. Four cycles of half‐sib family selection were conducted with from 63 to 276 families evaluated in a cycle. Family selections were based on mean visual top and root damage scores using a 1 to 5 visual rating scale. Four cycles of recurrent selection increased levels of 2,4‐D tolerance in red clover by approximately 35% with an average change of 0.30 score units per cycle. The narrow‐sense heritability of the 2,4‐D tolerance trait was near 50% and inbreeding depression was apparently minimal. These results showed that significant progress has been made and that future progress leading to economically valuable field tolerance should be possible.

Whole plant and tissue culture experiments were conducted to determine the difference in phytotoxicity of 2,4-D and its metabolite, 2,4-DCP, to red clover. At the whole plant level, the mean concentration of 2,4-DCP (10 mM) required to cause 50% growth inhibition (I50) of shoot dry weight was 24 times greater than for 2,4-D (0.42 mM). Using callus tissue, the I50value for 2,4-DCP (0.28 mM) was 22 times greater than for 2,4-D (0.013 mM) based on dry weights. The callus tissue was 36 and 32 times more sensitive to 2,4-DCP and 2,4-D than shoot tissue based on dry weights, respectively. These data indicate that 2,4-DCP was less phytotoxic than 2,4-D to red clover both in vitro and in vivo.

In vitro, selection is a viable method of selecting herbicide-tolerant crops. This research was to evaluate in vitro selection techniques for enhancing 2,4-D [(2,4-dichlorophenoxy) acetic acid] tolerance in red clover (Trifolium pratense L.). In vivo and in vitro responses to 2,4-D of eight diverse red clover populations were correlated (r=0.77), justifying in vitro selection for 2,4-D tolerance. Suspension cultures of a red clover genotype capable of regeneration were plated onto agar-based nutrient media supplemented with 0.18 mM 2,4-D for selection experiments. After two cycles of selection, 16 2,4-D tolerant callus lines were identified based on visual growth assessment. These lines were evaluated for 2,4-D tolerance (based on 2,4-D content), using a 2,4-D bioassay procedure which consisted of placing selected callus tissue pieces on top of oat (Avena sativa L.) coleoptile or internode sections. The relative amount of 2,4-D in the callus tissue was estimated by the amount of oat section elongation after 24 h. Two of the more tolerant callus lines had 61% and 83% less 2,4-D in their tissues than the susceptible control tissue. These studies indicated that in vitro selection can enhance the levels of 2,4-D tolerance in red clover callus tissue.

Root‐knot nematodes (Meloidogyne spp.) are a major limiting factor in the establishment and growth of many forage legumes, including alyceclover [Alysicarpus vaginalis (L.) DC.], which is highly susceptible to three Meloidogyne species. An extensive collection of Alysicarpus germplasm was evaluated for variability in Meloidogyne susceptibility to determine the feasibility of developing resistant cultivars. Germplasm was evaluated in two field (Arredondo fine sand) and two greenhouse tests. Variation in response to Meloidogyne spp. was identified in the Alysicarpus germplasm. Accessions FL‐1, FL‐4, FL‐5, and FL‐7 had overall mean gall scores of less than 2.0 (0 = no galls; 5 = more than 100 galls) when infested with M. incognita race 3. Accessions FL‐1, FL‐3, and FL‐4 received mean gall scores of less than 1.0 in response to M. javanica, while FL‐2, FL‐5, and FL‐7 had ratings of less than 2.0. M. arenaria race 1 was the most aggressive pathogen as only FL‐3 had a mean gall score of less than 2.0. No one line was highly resistant to all three Meloidogyne spp., suggesting the need for hybridization. Galling was highly correlated (r = 0.98) with egg mass production in the a!yceclover germplasm. Greenhouse and field results were also highly correlated (r = 0.61 to 0.89), so accessions resistant in the greenhouse were also field resistant. The level of Meloidogyne infestation achieved in Field Experiment 2 did not adversely affect yield, nodulation, or crude protein percentages. Broad sense heritabilities (47 ‐ 78%) indicate a large percentage of the existing variation is genetic. Thisuggests that hybridization and selection programs to improve populations could be successful.

Alyceclover [Alysicarpus vaginalis (L.) DC.] is a tropical legume considered to have poor seedling vigor. This characteristic often leads to difficulties in establishing new pastures. Ten Alysicarpus breeding lines were evaluated for early seedling growth and compared to common alyceclover. Field experiments in 1984 and 1985 at Gainesville, FL, on Arredondo fine sand (loamy, siliceous, hyperthermic Grossarenic Paleudult) detected a high degree of variation among genotypes for seedling vigor as measured by mean plant dry weights 3 and 6 weeks after planting. One line, FL‐3, was consistently more vigorous than common alyceclover. Several other lines (FL‐1, FL‐2, FL‐5, FL‐6, and FL‐11) were equal to or slightly less vigorous than the common type. Four lines (FL‐4, FL‐7, FL‐9, and FL‐10) had an unacceptable level of vigor. Within this collection of germplasm, there was a high correlation between seed weight and plant weight (r = 0.62 – 0.79). Visual ratings of seedling vigor taken 4 days after germination were also highly correlated with plant weights (r = 0.57 – 0.93). Seed weights and visual seedling vigor ratings may be useful characteristics for preliminary screening in future work. Broad‐sense heritabilities for plant dry weights were high (68–77%), indicating that seedling vigor may be under the control of genetic systems. It is suggested that improvement of alyceclover seedling vigor could be made via selection.