EVALUATION OF THE US CUCUMBER GERMPLASM COLLECTION FOR ROOT SIZE USING A SUBJECTIVE RATING TECHNIQUE

Root size in cucumber (Cucumis sativus L.) has received little researc h attention until recently. However, a large root system could improve nutrient and water uptake, and ultimately yield. Knowledge of root si ze could help cucumber breeders develop cultivars with improved perfor mance. A study was conducted in the greenhouse to evaluate 857 cultige ns (827 plant introduction accessions, 22 breeding lines, and 8 cultiv ars) of cucumber for root length. Complete data were obtained for 794 cultigens. Plants were grown from seeds in 2 replications in the green house. Plants were rated for root length using a 1 to 9 scale (1-3 = s mall, 4-6 = medium 7-9 = large). Also, root length was measured from s oil surface to the tip of the longest main root. In addition, all cult igens were evaluated for root length and dry weight to provide meaning to the subjective rating. Root rating was highly correlated with both root length (r = 0.92) and dry weight (r = 0.64) of roots. Root lengt h averaged 74 mm and most cultigens (579, or 68%) had roots 40 to 110 mm long. The cultigen with the longest roots was PI 183056 (193 mm), a nd the shortest was PI 176954 (2 mm). The subjective rating technique provided a simple, accurate and rapid method to estimate root growth i n the greenhouse.