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Josh H. Freeman, Stephen M. Olson and Eileen A. Kabelka

between the two cultivars. This suggests that there may be other factors that contribute to a pollenizer's performance. Pollen viability could be a determining factor in the performance of watermelon pollenizers. Pollen flow from a pollenizer would be of

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Cary Hebert*, Jeff Kuehny, Charles Johnson and Annina Delaune

The genus Clerodendrum belongs to the family Verbenaceae of which there are over 400 tree, shrub, and vine species. Species of Clerodendrum vary in leaf size, shape and texture; inflorescence shape; and flower shape, size and color. There is commercial interest in developing hybrids with desirable floricultural attributes. Interspecific hybridization could be used to increase variability in flower color, inflorescence shape, plant vigor, leaf color and shape for selection. Pollen viability among species is in question because of absence of seed set on many selected plants. The need for assessing viability of pollen used is important in determining the strategies to be used in hybridization. Clerodendrum floribundum, C. speciosissimum, C. splendens, C. × speciosum (C. thompsonia × C. splendens) and C. quadriloculare grown in a greenhouse under natural daylight were used as pollen sources. Pollen was collected from recently opened anther, placed in a scintillation vial on ice, and brought into the laboratory. A peroxidase test, dehydrogenase test, and the fluorescein diacetate procedure were used to determine percent viability of pollen before, during and after anthesis for each Clerodendrum species.

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Raphael A. Stern and Shmuel Gazit

The lychee (Litchi chinensis Sonn.) has two types of pollen-releasing flowers—M1 and M2. We compared the morphology and viability of these two pollen types, mainly for the two commercial cultivars in Israel: `Mauritius' and `Floridian'. Observation by scanning electron microscope did not reveal any consistent morphological differences between the two pollen types. However, M2 pollen was found to have a consistent and significant advantage over M1 pollen in in vitro germination tests. M2 pollen from `Mauritius', `Floridian', `No Mai Chee', `Wai Chee', and `Early Large Red' had a much higher germination rate at 15, 20, 25, 30, and 35 °C than M1 pollen from those same cultivars. The optimal incubation temperature for in vitro pollen germination was 30 °C for M2 pollen of all five cultivars studied; adequate germination rates were also found at 35 and 25 °C. The optimal temperature for M1 pollen germination was also 30 °C for `Mauritius' and `No Mai Chee', but was not well defined for the other three cultivars. No pronounced advantage of M2 pollen-tube growth could be discerned 48 h after hand pollination. However, final fruit set was consistently and significantly higher after hand pollination with M2 pollen, relative to M1 pollen. Hot (32/27 °C) and warm (27/22 °C) regimes during flower development had a pronounced detrimental effect on pollen viability compared to a cool (22/17 °C) regime. `Floridian' was much more susceptible than `Mauritius' in this respect.

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Cecilia E. McGregor and Vickie Waters

because they can be readily crossed with watermelon cultivars, they are obvious candidates for use in breeding programs. However, high levels of marker segregation distortion, low fruit set, and diminished pollen viability have been observed in mapping

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Kauahi Perez

first-hand experience on how to apply a concept for themselves. The concept of pollen viability is a critical component in the field of plant breeding and can be used to explain various phenomena of plant breeding as they relate to pollen quality. Pollen

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Hamidou F. Sakhanokho and M. Nurul Islam-Faridi

appear to be diploid (2 n = 2 x = 24). The effect of induced polyploidy has been associated with modifications of various traits including plant height, flower size, pollen viability, fruit characteristics, and leaf size ( Chen et al., 2006 ; Kermani

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Aref A. Abdul-Baki

A procedure is described for determining pollen viability in tomatoes (Lycopersicon esculentum Mill.) by growing pollen in a growth medium containing 0.29 M sucrose, 1.27 mm Ca(NO3)2, 0.16 mm H3 BO3, and 1 mm KNO3 (pH 5.2) to which 0.001% fluorescein diacetate (FDA) was added. Pollen viability can be evaluated within 30 min by determining percent fluorescing pollen in a sample. The procedure further allows the determination of percent germination in vitro and pollen tube growth within 1.5 hours. Neither the germination medium nor FDA has any adverse effects on germination and pollen tube growth. Percent fluorescent pollen and percent total pollen germination were highly correlated, suggesting that fluorescence is a good measure of pollen viability. The combined fluorescence-germination procedure is simple and adapted to routine screening of many samples.

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Scott Reid, Judy Harrington and Harrison Hughes

Distichlis spicata var. stricta (Torrey) Beetle is a native grass that tolerates salt, high pH, and some heavy metals. It has been proposed for use in several challenging environments, including mine spoils and salt-impacted areas of golf courses. But, its widespread use has been hindered by several factors, one of which is poor seed set. Because chromosome numbers are variable and some genotypes are aneuploids, there was concern that pollen viability in some genotypes was low. Pollen from several genotypes failed to germinate in vitro on four artificial media prepared with various levels of osmoticum. However, hand pollination in vivo resulted in profuse pollen germination for all genotypes tested. Germination on pollinated stigmas was observed at intervals beginning 2 h after pollination with a fluorescence microscope using aniline blue and acridine orange stains and in bright field using toluidine-O stain. Very young stigmas seemed unreceptive and, while pollen would germinate, the pollen tubes would not grow down through the style. On receptive stigmas, many pollen tubes grew down toward the egg and some reached it within 24 h. There was no evidence of impaired fertility. Aniline blue was the best method for observing pollen tube growth through the style, although toluidine-O was adequate for observing germination on the stigmatic surface.

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Marijana Jakše, Pablo Hirschegger, Borut Bohanec and Michael J. Havey

), sugar content and potassium concentration of flower nectar ( Hagler, 1990 ; Lederhouse et al., 1968 ), and pollen viability ( Nye and Waters, 1971 ; Ockendon and Gates, 1976 ). In general, onion inbred lines are only partially homozygous because only a

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Ann M. Chanon, Pablo S. Jourdan and Joseph C. Scheerens

The genus Aesculus (buckeyes and/or horsechestnuts) is composed of 13 species and a number of interspecific hybrids. Pollen from 11 genotypes from five Aesculus species and the hybrid Aesculus ×carnea were used to develop an in-vitro germination test to evaluate pollen viability under various storage treatments. This test was optimized using samples of both fresh pollen and pollen that had been stored up to 1 year. The most effective medium contained 20% sucrose, 100 mg·L-1 H2BO3, 150 mg·L-1 Ca(NO3)2, and 1% agar. The highest germination percentage was observed at 15 °C across all storage treatments. Fresh pollen germinated in excess of 80% over a wide range of germination temperatures. Based on this, all specimens studied would be good pollen parents. The differences in pollen germination between storage at -20 and -80 °C were nonsignificant, but the duration of the storage period was highly significant. At 3 months, viability remained above 60% for four of the six species/hybrid tested. However, at 12 months, all pollen tested dropped below the threshold for good fruit set based on in-vitro pollen germination. Based on these observations, short-term pollen storage may permit crosses between parents with temporally separate flowering phenologies. However, conventional storage procedures are inadequate to maintain pollen collected from a male parent for crosses in subsequent growing seasons.