Chlorophyll Content of Persistent - Green and Normal Snap Bean Pods ( Phaseolus vulgaris L

Chlorophyll concns decreased rapidly as pods matured from the 1-day-old fruit stage. Total ' chlorophyll a + b per pod was influenced by pod length as well as pigment concn. Apparent chlorophyll synthesis occurred in field-grown green snap bean fruits up to 11-mm diam pods (sieve size 5 or 6), but a net decrease occurred with further maturation. Dry-mature persistent-green pods contained 300 ppm chlorophyll on a dry matter basis, whereas normal-green pods had none. Lack of consistent agreement between visual and chemical methods to rank cultivars for pod color suggested differences in chlorophyll distribution in external versus internal tissue. Color intensity in green snap bean pods decreases with increasing pod size and physiological maturity. Loss of green color may parallel increases in fiber (texture) and seed content, and decreases in other quality factors. Decreased color intensity creates a serious problem for commercial processors since color influences the esthetic quality (4). Utilization of the persistent-green character (PC) in snap beans (for processing) has been suggested (3) as a means of increasing color uniformity among pods of various physiological maturities. Intensity of the green color decreases more rapidly with physiological aging in normal than in PC pods. It was assumed that chlorophyll concns were correlated with pod color, hence the chlorophyll loss from developing pods of normal cultivars would be much more rapid than in PC Pods. It was anticipated that small immature pods of PC and normal lines might not differ greatly in chlorophyll concn. Visual evaluation of large pods, however, suggested that PC lines had greater chlorophyll concns than normal cultivars. This becomes apparent at seed maturity when PC pods remain green while normal-green pods become tan or light brown. The large-sieve and mature PC pods remain green longer possibly because chlorophyll does not degenerate as rapidly as in normal pods, a fact that has already been established for excised leaves from these plants (2). Persisent green pods may be able to synthesize chlorophyll for a longer period of time than do normal-green cultivar pods. Another possibility is that the enzyme which destroys chlorophyll may be inactivated in the PC pods while some chlorophyll yet remains. Bouwkamp and Honma (2) postulated 'Received for publication January 19, 1971. Joint contribution from the Northwest Branch, Soil and Water Conservation Research Division, Agricultural Research Service, USDA; and the Idaho Agricultural Experiment Station. Approved by the Director, Idaho Agricultural Experiment Station as Research Paper No. 846. 2Research Soil Scientist, Snake River Conservation Research Center, Kimberly, Idaho and Research Professor of Plant Pathology, Bean Research Laboratory, University of Idaho, Twin Falls, respectively. 3Hildebolt, W. M. 1969. The influence of preservation methods of the color and other quality attributes of green beans (Phaseolus vulgaris L.). Unpublished Ph.D. Thesis, Ohio State University. that leaves from PC plants contained higher endogenous levels of some kinetin-like substance than did leaves from normal cultivars. This could explain the greater tendency of PC lines to abscise older leaves following plant stress, but it is not clear how this might affect rates of chlorophyll formation or degradation in pods. The objectives of this study were to identify the differences in chlorophyll yield components between several PC breeding lines, and normal-green snap bean cultivars, and secondly, to determine if ranking by chlorophyll concn correlated with visual color grading of pods. Materials and Methods Pods were harvested from 4 experimental PC lines and 2 normal-green snap bean cultivars grown during 1969 under irrigation at the Twin Falls, Idaho Branch Experiment Station. The experimental lines were XIda 121-15-3 (since named `Custer'), Xlda 69-3, XIda 266-5, and Xlda 68-5381, while the normal-green cultivars were 'Tendercrop' and 'White Seeded (WS) Tendercrop'. The pods were harvested August 11, 52 days after planting, immediately hand-graded to sieve sizes 3 and under, 4, 5, 6, and 7 and over, and randomly divided into 8 subsamples each containing 10 to 14 pods (6 to 8 g total dry wt). Sieve sizes 1, 2, 3, 4, 5, 6, and 7 and over correspond to <5.8, 5.8 to<7.3, 7.3 to <8.3, 8.3 to <0.5, 9.5 to <10.7, 103 to <11.7 and >11.7 mm diam, respectively. Pods were weighed and then freeze-dried to less than 0.5% water content and reweighed. The freeze-dried material was ground to pass a 40-mesh sieve and stored in plastic vials at —20C until analyzed. In a second experiment, Xlda 69-3 and `WS Tendercrop' were grown under winter greenhouse conditions. Harvested samples consisted of the following pod sizes: 2(1-day-old), 3-, and 3-5-mm diam, sieve sizes 1 to 5; nearly mature (30% dry matter); and mature (85% dry matter). Samples were treated similarly to those collected from the field. In another experiment, pods from 10 green snap bean lines grown under field conditions were harvested at sieve size 6, 362 J. Amer. Soc. Hort. Sci. 96(3):362-365. 1971.