IMPROVEMENT OF DISPLAY LIFE OF BIG BEND BLUEBONNET RACEMES BY RECURRENT PHENOTYPIC SELECTION

The key components affecting postharvest vase life in Big Bend bluebonnet (Lupinus havardii Wats.) are flower abscission and flower senescence which appear to be related to sensitivity of the germplasm to ethylene. We have used recurrent phenotypic breeding/selection techniques, including traits of low shattering and long display life of flowers on the racemes, to develop several blue, white, and pinkcolored lines and cultivars of bluebonnet with reduced ethylene sensitivity and extended vase life. The relative response of the germplasm to ethylene was evaluated following treatment with 2-chloroethylphosphonic acid in the holding solution. Among genotypes tested, the advanced white-flowered line (WS02) exhibited the least sensitivity to ethylene, while the blue cultivar ‘Texas Sapphire’ was found to be the most sensitive. The improved breeding lines show very little or no abscission of flowers in response to ethylene. These results clearly establish the important role of selection and breeding strategies in the improvement of bluebonnet as a cut flower. INTRODUCTION Over the years, cut flower demand has continued to increase but domestic production has not kept pace with the growing and varied market demand. This underscores the importance of new crops in maintaining and expanding market share in the cut flower and pot plant market (Halevy, 1999). As such, new specialty cut flower crops have immense potential to expand production acreage and increase sales. The term ‘bluebonnet’ is used in Texas to describe plants that most horticulturists elsewhere refer to as ‘lupines’ (Davis et al., 1994). Bluebonnet is considered an important symbol of Texas and all six native Lupinus species have official state flower status. Lupinus havardii Wats. (Big Bend bluebonnet) is native to a narrow geographical range along the Rio Grande River in southwestern Texas, and produces tall blue, fragrant racemes (Davis et al., 2000). A research project to evaluate the cut flower potential of L. havardii was started in 1991. The initial focus was to improve crop uniformity and develop novel flower colors. Other traits that were used for selection included low shattering and long display of flowers on the intact raceme to improve vase life. Subsequently, we discovered that the key components affecting postharvest vase life of cut racemes in L. havardii are flower abscission and flower senescence which appear to be related to sensitivity to ethylene (Mackay et al., 2001). Recently, inheritance and response to selection for improved vase life of flowers have been studied in gerbera (Wernett et al., 1996), Asiatic hybrid lilies (van der Meulen-Muisers et al., 1999) and carnation (Onozaki et al., 2001). This report describes some of our results relating to the development of bluebonnet cultivars and advanced breeding lines with reduced ethylene sensitivity and extended vase life using recurrent phenotypic selection. MATERIALS AND METHODS Plant Material Populations of L. havardii occur sporadically in a narrow range in a remote area along both sides of the Rio Grande River in Texas and Mexico. In this area, several years may pass before there is sufficient rainfall to support significant populations. Flowers are generally violet-blue, but rarely white or pink flowered plants are also found. Since 1991, Proc. VIII IS Postharvest Phys. Ornamentals Eds. N. Marissen et al. Acta Hort. 669, ISHS 2005 208 we have been closely monitoring the populations and have enriched our seed diversity for breeding efforts. As described previously, we now routinely grow Big Bend bluebonnet plants in non-shaded greenhouses at Dallas, Texas. Several crops can be grown and evaluated in the greenhouse each year (Davis et al., 2000). Crossing and Selection Our breeding efforts are aimed at 1) developing genotypes with novel and uniform flower colors, 2) improved vaselife, 3) ethylene insensitivity or reduced ethylene production and 4) improved response to shipping. In its native habitat, L. havardii requires insects, primarily honey bees and bumble bees, for pollination. However, in the greenhouse, hand pollination is readily accomplished with camel hair artist paint brushes. The plants can be easily selfed and thus rapid progress can be made in isolating recessive genes. In breeding for improved display life, we have used recurrent phenotypic selection, including traits of low shattering and long display life of flowers on intact racemes. Breeding efforts have now been carried out for more than 10 generations. Vase Life Evaluation Different cultivars and breeding lines of L. havardii were grown in the greenhouse by standard production methods. Immediately after harvest, the freshly cut racemes were brought to the laboratory for vase life evaluation. An aqueous solution of desired concentration of ethephon (2chloroethylphosphonic acid, CEPA) was used a source of ethylene. Cut racemes were transferred to glass vases containing either 400 ml of water or an equivalent amount of freshly prepared solution of CEPA at 22±2oC under cool white florescent lamps (30 μmol·m·sec). The number of abscised and senescent flowers, in control and in the presence of CEPA (100 μM) was recorded regularly, and vase life evaluated. RESULTS In the wild, plants with violet-blue flowers predominate. Occasionally, plants with white or pink flowers are also found in the frequency of ~1 in 10,000 for white and ~1 in 100,000 for pink. In 1992, we collected seed from pure uniform violet-blue populations, seed from four plants that were nearly white, and seed from one pink plant. When we grew the first populations in the greenhouse, we noted that there were two distinct types of plants. One type exhibited flower shattering within a few days of opening and the other type held the flowers on the raceme for a relatively long period of time. Racemes harvested from the two types exhibited the same behavior in the vase with one shattering quickly and the other exhibiting a relatively long vase life. As such, flower retention on the intact raceme became one of the characteristics that we used in our breeding effort through phenotypic recurrent selection. Within each breeding line, we routinely would select 300 seedlings based on vigor from 1000 that had been grown and then select 3-5 plants from the 300 plants that were grown from the selected seedlings for crossing or selfing, depending upon the line. Through repeated selection each year, we obtained the improved cultivars ‘Texas Sapphire’ and ‘Texas Ice’ which are violet-blue and white flowered respectively (Mackay and Davis, 1998). Subsequently, these cultivars have been further improved and refined. It is significant to note that both the ‘blue flowered’ and ‘white flowered’ breeding lines represent unbroken genetic lines derived from the initial germplasm collected in the wild in 1992. As such, ‘BS02’ is the latest effort in improvement of ‘Texas Sapphire’ and ‘WS02’ is the latest effort in improvement of ‘Texas Ice’. The genetic history of the ‘pink flowered’ line is somewhat complicated. In contrast to the blue and white flowered lines, we only had one plant to begin our breeding efforts. That plant had some undesirable traits such as lateness in flowering and susceptibility to disease and insects. We were unable to improve the time to flowering and