EVALUATION OF DENDROBIUM CROSSES
INVOLVING FOUR NEW AMPHIDIPLOID PARENTS

Abstract

Four new amphidiploid dendrobium plants became available for breeding: K706-18 and D184-4N, having Dendrobium discolor in their background, and K916-57 and K927-27, having D. gouldii in their background. Twenty-four crosses were made utilizing the four amphidiploids to possibly identify cross combinations that might complement existing cultivars in reducing the peaks and valleys of seasonal flower yields.

Among the eight progenies involving K706-18 as a parent, K1299 (K706-18 x D. Jaquelyn Thomas D192) gave the best results and therefore will be released for trail by growers. K1323 (K706-18 x D. Jaquelyn Concert D239-1), which produced attractive red flowers, will be recommended for trial as potted plants. K1430 (D184-4N x K916-57), K1426 (K440-50 x K916-57), and K1427 (K927-27 x D168-12) produced the best results among their related crosses. These crosses will be offered to growers for trail to complement the commercial cultivars UH232, UH503, and UH507 in broadening seasonal yields.

Introduction

Evaluation of the dendrobium crosses to develop new cultivars for commercial cutflower production has been an ongoing activity of the dendrobium breeding program at the University of Hawaii. In 1989 the results of an experiment comparing 16 seed-propagated amphidiploid dendrobium progenies were summarized (Kamemoto et al., 1989). The cross UH800 (‘Uniwai Mist’) combined many desirable characteristics and therefore was released to dendrobium growers to complement the cultivars UH44 (‘Uniwai Blush’), UH232 (‘Uniwai Supreme’), UH306 (‘Uniwai Pearl’), UH503 (‘Uniwai Prince’), and UH507 (‘Uniwai Princess’) developed earlier (Kamemoto 1985, Kamemoto et al. 1976, Kamemoto and Bobisud 1979, Kamemoto and Kunisaki 1980, Kamemoto and McConnell 1982).

A few new amphidiploid plants have become available for breeding, namely K706-18 (D. Manoa Ruby), D184-4N (D. superbiens), K916-57 (D. Jaquelyn Thomas), and K927-27 (D. Jaquelyn Thomas). These amphidiploids were crossed to several other amphidiploid plants in hope of identifying desirable new cross combinations that might complement existing cultivars in reducing the peaks and valleys of seasonal yields.

Materials and Methods

New amphidiploid parent plants

The origin and genome characteristics of the four new amphidiploid breeding plants are as follows:

Crosses

The parent plants used in producing 24 crosses with the four new amphidiploid plants are listed in Table 1, along with their registered hybrid names and origins. Two University of Hawaii cultivars released earlier UH232 and UH503, served as controls. Pollinations with K706-18 were made between February and May 1988 while all other pollinations were made between January and April 1991. Seeds were germinated aseptically about three months after pollination, and seedlings were transflasked three months later. Seedlings were transplanted into community pots about six months after germination, and into 2-inch pots about six months later. About 9 to 10 months later, seedlings were moved into 6-inch black plastic pots containing no. 3 crushed blue rock as a medium.

The amphidiploid progenies were arranged on benches in a polypropylene shadehouse (30 percent shade). Twenty-two plants per cross were observed.

Raceme (spray) yield was recorded weekly for K706-18 progenies from July 1990 until December 1993, while progenies of the other three amphidiploids were observed from June 1993 to June 1996. Scape length was measured from the point of attachment to the pseudobulbs to the lowest flower, while raceme length was measured from the point of attachment to the pseudobulbs to the tip of the raceme. Other flower characteristics measured were flower width, pedicel length, number of flowers per raceme, and percentage bud drop. The vase life was expressed as the number of days until 50 percent of the flowers on the raceme wilted or dropped off. At the end of the experiment the height of the tallest pseudobulbs was recorded.

Data were analyzed using SAS software (SAS Institute, Cary NC). Analysis of variance was conducted for each characteristic using the general linear model procedure. Bud drop percentage was transformed with the arc sine transformation prior to analysis. Differences among treatment means at the 95% probability level were calculated using Duncan’s multiple range test.

Results and discussion

Crosses with K706-18

No differences were observed for raceme length, but statistically significant differences were observed for scape length. However, the magnitude of the differences were small, and they probably do not have any practical significance.

The number of flowers per spray was about equal for most crosses, except for K1304 and K1306, which had fewer flowers. Flower size expressed as flower width (natural spread of flowers) was largest for K1290, K1299, and K1302, which had K159-21, D192, and K159-19, respectively as the second parent. The pedicel was longest in K1299, undoubtedly an influence of the D192 parent.

With the exception of K1323, with a vase life of 14.5 days, the vase lives of 16.9 to 19.6 days for all other crosses did not differ statistically. Bud drop percentage was less than 1.5 for all crosses. The pseudobulb height showed variation, from 106.4 cm for K1299 to 72.1 cm for K1308.

Slight variation in flower size and color was observed among individuals within progenies. Both K1299, with red-purple (RHSCC 72B) flowers, and K1323, with dark red-purple (RHSCC 71A) flowers, showed slight variation among offspring.

Based on all characters enumerated above, two crosses appear worthy of trial by growers. K1299, a cross between K706-18 and Jaquelyn Thomas D192, produced long racemes, numerous flowers per raceme, relatively large flowers, fairly uniform flower color, good vase life, and a low bud drop. A weakness might be the tall pseudobulbs. The performance of K1299 was equal to that of the control, K1281 (UH232). The seasonality is shown in Figure 1. K1299 might well complement the cultivar UH503 (‘Uniwai Prince’), which is now under commercial production.

The major attribute of K1323 is the attractive, reddish-purple flower resulting from the combination of dark purple (K706-18) and bright reddish-purple (Jaquelyn Concert, D239-1). Unfortunately, the vase life of K1323 is shorter than the other crosses. Because of attractive “red” flowers, K1323 was released earlier for trial. As shown in Figure 1, flowering is spread throughout the year, without the pronounced peaks of other PPCC-type cultivars. Perhaps K1323 is better suited as a potted plant cultivar than as a cutflower cultivar.

Crosses with D184-4N

Some variation in size and color of flowers was observed within progenies. K1431, having NH-4N as a parent, showed greater variation among offspring than other crosses. K1442, having K706-18 as a parent, produced several distorted racemes.

K1444, having K44-50 as a parent, and K1430, having K916-57 as a parent, outperformed all crosses including the control, K1440 (Uh503). Raceme yield, number of flowers per raceme, and seasonality were similar (Fig. 2). Because the flower color of K1430 was slightly darker purple than that of K1444, and similar to that of UH503, K1430 will be recommended for trial by interested growers.

Crosses with K916-57

The results of crosses with K916-57 (D. Jaquelyn Thomas K916-57) are presented in Tables 6 and 7. K1426, having K44-50 as a parent, along with the reciprocal cross (K1441) outperformed UH232 (K1439) in raceme yield, raceme length, and number of flowers. The crosses having 0580-4N as a parent (K1412, K1432, K1438) had fewer flowers and flowers with shorter pedicels than the crosses involving K44-50. The size of the flowers, vase lives, and bud drop percentage of all crosses did not differ.