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Inheritance of male-sterility and dwarfism in watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai]
Scientia Horticulturae 74 Ž1998. 175–181
Inheritance of male-sterility and dwarfism in watermelon w Citrullus lanatus žThunb. / Matsum. and Nakai x Huang Hexun ) , Zhang Xiaoqi, Wei Zhencheng, Li Qinghuai, Li Xi Agro-biotechnical Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, People’s Republic of China Accepted 24 July 1997
Abstract Preliminary studies of a dwarf, male-sterile watermelon showed that male-sterility was controlled by a pair of recessive nuclear genes; it appeared simultaneously with dwarfism and its dwarf gene was different from the three known dwarf genes. Pollen aborted completely in male-sterile plants. Potential uses for the dwarf, male-sterile watermelon are also discussed. q 1998 Elsevier Science B.V. Keywords: Dwarfism; Male-sterility; Watermelon; Gene
1. Introduction Heterosis has played an important role in watermelon production, yet hybrid seed production in most countries still follow a complicated procedure of emasculating, bagging, and pollinating by hand. The procedure is troublesome and time-consuming and it is difficult to guarantee the purity of watermelon hybrid seeds. The use of male-sterility is the best way to solve the problem. Since Watts Ž1962. first obtained a male-sterile watermelon by irradiation, much attention has been paid to the use of male-sterility. Xia et al. Ž1988. found a naturally occurring male-sterile watermelon Abbreviations: DMSW, dwarf, male-sterile watermelon; MFPs, male fertile plants; MSPs, male-sterile plants; HMFPs, heterozygotic male-fertile plants ) Corresponding author. Tel.: q86 20 87596508; fax: q86 20 87503358. 0304-4238r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 4 2 3 8 Ž 9 7 . 0 0 1 0 2 - 7
176
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
mutant which Liu et al. Ž1991. used in their breeding programme and varieties developed by them have now been released. In 1989, the authors discovered a naturally occurring dwarf, male-sterile mutant in an introduced watermelon population. The use of this dwarf, male-sterile watermelon should simplify the production of hybrid seeds and thus, lower its cost. In this report, we investigated male-sterility, its mechanism and the dwarf gene of the dwarf, male-sterile watermelon.
2. Materials and methods 2.1. InÕestigation of the male-sterile gene and its genetic pattern In test 1, the dwarf, male-sterile watermelon ŽDMSW. was crossed with three cultivars, namely ‘Changhui’, ‘Fuyandagua’ and ‘America B’, and the fertility of the offspring in the F1 and F2 generations was investigated. In test 2, the pollen of male-fertile plants ŽMFPs. was used to fertilize pistillate flowers of male-sterile plants ŽMSPs. of the same plant line; the fertility of the offspring was also investigated. 2.2. InÕestigation of the dwarf gene The DMSW was crossed with ‘Sugar Bush’ and ‘Xinjiang Dwarf Watermelon’, and the height of the offspring in the F1 and F2 generations was investigated. 2.3. Breeding of a dual-purpose line Pollen of heterozygotic male-fertile plants ŽHMFPs. was used to pollinate pistillate flowers of MSPs of the same plant line, and seeds from the MSPs were collected. The offspring obtained were 50% HMFPs and 50% MSPs. This dual-purpose line can, therefore, propagate and maintain the male-sterile line by repeatedly crossing MSPs with HMFPs of the same plant line. 2.4. Cytological studies Staminate buds at different development stages were picked from HMFPs and MSPs of the dual-purpose line and immediately fixed in Carnoy fixative. Microspore development was investigated by the smearing technique using acetocarmine as staining agent. The structure of the anthers was investigated by paraffin microtomy using safranine as staining agent. 2.5. Chromosome obserÕations Young leaves of HMFPs and MSPs of the dual-purpose line were taken, fixed in Carnoy fixative and treated with a mixed enzyme solution of 3.0% cellulase and 2.5%
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
177
pectinase for 2 h at 258C. The treated leaves were smeared and chromosomes were counted under a microscope using acetocarmine as staining agent.
3. Results 3.1. Study of male-sterility DMSW plants differ greatly in morphology from normal plants ŽFig. 1.. DMSW is about 1.5-m tall with fewer leaf lobes Žfewer lobes leaf is between normal leaf and non-lobes leaf. than normal plants and could readily be identified by its leaf characteristics when 2–3 true leaves were present. Bud size of the DMSW only varied a little at different development stages. Most of the staminate flowers did not open. Of the staminate flowers that did open, most of the anthers were greenish yellow or brown. It seemed that the development of the male organs had been somehow stunted. To make use of male-sterility, it is imperative to know its genetic pattern. Table 1 shows that the ratio of MFPs and MSPs in the F2 generation in all three combinations conformed to a 3:1 segregation rate. Table 2 shows that the ratio of HMFPs and MSPs in the offspring of backcrosses conformed to a 1:1 segregation rate, from which it could be inferred that male-sterility of DMSW is controlled by a pair of recessive nuclear genes. Because of the simultaneous appearance of male-sterility and dwarfism, we name the male-sterile gene as ms d w , its genetic model is as Figs. 2 and 3. Observations of on anthers at different developmental stages from MSPs showed that the development of male-sterility differed among individual plants. Tetrads of some
Fig. 1. Comparison of DMSW Žright. and normal plants Žleft..
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
178
Table 1 Fertility segregation in the F2 generation Combinations
Number of plants
DMSW=‘Changhui’ DMSW=‘Fuyandagua’ DMSW=‘America B’
In total
Male-fertile
Male-sterile
103 104 63
75 78 44
28 26 19
Male-fertile:male-sterile
X 2 value
2.7:1 3:1 2.3:1
0.1586 0.0128 0.6402
2 X 005.1 s 3.84.
anthers congregated in the tetrad stage and failed to develop into normal pollen grains; while other anthers developed normally until the mid-monokaryon stage, and then the pollen began to wrinkle and was aborted. No matter when pollen abortion took place, no pollen grains or only a few empty pollen grains were present in the anther chambers when the flowers bloomed and the pollen was completely aborted. Observations of the structure of the anthers of MSPs by paraffin microtomy showed that there was abnormal partial increment of tapetum which was one of the reasons that made pollen abort early because the microspores were squeezed. This did not occur in the anthers of MFPs. Because of the similarity between seeds of the MSPs and multiploids, the chromosomes of MSPs were examined to see if male-sterility was caused by a change in chromosome number. The results showed that MSPs had the normal number of chromosomes ŽTable 3.. 3.2. Study of the dwarf gene of DMSW So far, three dwarf genes of watermelon Ž dw-1, dw-1s, dw-2 . have been reported; dw-1 and dw-1s are allelic while dw-1 and dw-2 are non-allelic ŽLin, 1992.. In one of our tests, DMSW was crossed with normal plants and all plants in the F1 generation were normal, while the ratio of normal to dwarf plants in the F2 generation conformed to a 3:1 segregation ratio. In another test, DMSW was crossed with both ‘Sugar Bush’ Ž dw-1dw-1. and ‘Xinjiang Dwarf Watermelon’ Ž dw-2dw-2 .. All the plants in the F1 were normal, while in the F2 , there were dwarf plants and DMSW in addition to normal plants. When some dwarf plants were self-fed, DMSW appeared in the offspring, while in the offspring of cross between some DMSW and dwarf plants in the same plant line, only DMSW and dwarf plants appeared. From these results, it could be inferred that
Table 2 Fertility segregation in the offspring of a backcross Combinations
DMSW=HMFP1 DMSW=HMFP2 2 X 0.05.1 s 3.84
Number of plants In total
Male-fertile
Male-sterile
15 11
8 6
7 5
Male-fertile:male-sterile
X 2 value
1.1:1 1.2:1
0 0
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
179
Fig. 2. Fertility gene segregation in the F2 generation.
there is a new dwarf gene Ž dw-3 . in watermelon in addition to three reported dwarf genes. This dwarf gene appears simultaneously with male-sterility and its expression seems to be concealed by dw-1 and dw-2. The relationship among four dwarf genes needs further investigation. 3.3. Breeding of dual-purpose line Generally, a two-line method is adopted in order to make use of nuclear male-sterility. Excellent multi-typic dual-purpose line is the basis of application. Cross MSPs with watermelon material of good agricultural characteristics and screen the plant lines whose offspring show 1:1 ratio of HMFPs and MSPs. In such a plant line, sister cross between MSPs and HMFPs is made. With such cycling cross and selection, stable dual-purpose line can be obtained. So far, four types of male-sterile line have been developed by such methods: Ža. light green rind, elongate fruit, male-sterile line; Žb. black rind, round fruit, male-sterile line; Žc. dotted rind, round fruit, male-sterile line; Žd. light green rind, round fruit, male-sterile line. Because the original MSPs had fewer seeds per fruit Ž50–100 seeds per fruit. than normal fertile plants, the problem of how to increase the number of seeds per fruit of MSPs is also one of the objective of breeding the dual-purpose line. Improved MSPs with more seeds per fruit have been obtained to some extent, with the highest number of seeds per fruit being 360. Our experiments showed that selection of
Fig. 3. Fertility gene segregation in the offspring of a backcross.
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
180
Table 3 Comparison of chromosome numbers in MSPs and HMFPs Plant type
Number of cells with 22 chromosomes 44 chromosomes
Other numbers of chromosomes
Percentage of cells with 22 chromosomes
MSPs HMFPs
22 30
0 0
100 96.9
0 1
watermelon materials with a high number of seeds per fruit as a parent was an effective way to improve the number of seeds per fruit of MSPs.
4. Discussion So far, several male-sterile watermelon have been reported. Because it is not necessary to match three-line combinations and a potent recovery line is easy to obtain, application of watermelon male-sterility has become hot topic of watermelon breeding and is getting more and more attention. How to maintain male-sterile line and identify MSPs in a mixed population in early stages should be solved before male-sterility can be used in breeding programmes. In DMSW, male-sterility appears simultaneously with dwarfism and fewer leaf lobes. Dwarfism makes it possible to increase planting density
Fig. 4. Model for maintaining the male-sterile line and hybrid seed production with a dual purpose line.
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
181
and thus, to increase seed production per unit area. Fewer leaf lobes is a marker. So, DMSW is a very valuable male-sterile material. In order to make use of DMSW, two-line methods can be adopted, i.e. select a stable dual-purpose line which shows 1:1 ratio of MSPs and HMFPs in the offspring population. The dual-purpose line can propagate and maintain the male-sterile line. When dual-purpose line is used to maintain the male-sterile line, pollen of HMFPs is used to pollinate stigmas of MSPs in the same dual-purpose line, seeds in MSPs are collected and its offsprings will still show 1:1 ratio of MSPs and HMFPs. When dual-purpose line is to be used in the hybrid seed production, the planting density is doubled, and HMFPs are eradicated in the seedling stage according to leaf characteristics, the remaining plants are MSPs. When MSPs are planted with recovery line alternately, pollen of recovery line will pollinate the stigmas of MSPs. Seeds collected from MSPs can be used in watermelon production. This seed-production method gets rid of the troublesome procedure of emasculating, bagging, and pollinating by hand. Its maintaining and seed-production model is as Fig. 4. If a diheterozygotic maintaining line can be developed using chromosome translocation techniques ŽPatterson, 1973., application of DMSW would be more effective.
References Lin, D.P., 1992. Gene directory of watermelon Ž1991. Žin Chinese.. Translated from CGC report ŽAugust 1991.. China Watermelon and Muskmelon, 2, pp. 1–4. Liu, Y.A., Chen, A.B., Wu, X.L., 1991. Application of male-sterile dual-purpose line of watermelon G17AB. China Watermelon Muskmelon 2, 6–10, in Chinese. Patterson, E.B., 1973. Proc. 7th Meeting Maize and Sorghum Seet. Eucarpia, Sept. 3–6. Zagreb, Yugoslavia. Watts, V.M., 1962. A marked male-sterile mutant in watermelon. Proc. Am. Soc. Hort. Sci. 81, 498–505. Xia, X.T., Liu, Y.A., Liu, E.J., Chen, A.B., 1988. Selection of dual-purpose male-sterile line of G17AB watermelon. J. Shenyang Agric. Univ. 19 Ž1., 9–13, in Chinese.
Inheritance of male-sterility and dwarfism in watermelon w Citrullus lanatus žThunb. / Matsum. and Nakai x Huang Hexun ) , Zhang Xiaoqi, Wei Zhencheng, Li Qinghuai, Li Xi Agro-biotechnical Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, People’s Republic of China Accepted 24 July 1997
Abstract Preliminary studies of a dwarf, male-sterile watermelon showed that male-sterility was controlled by a pair of recessive nuclear genes; it appeared simultaneously with dwarfism and its dwarf gene was different from the three known dwarf genes. Pollen aborted completely in male-sterile plants. Potential uses for the dwarf, male-sterile watermelon are also discussed. q 1998 Elsevier Science B.V. Keywords: Dwarfism; Male-sterility; Watermelon; Gene
1. Introduction Heterosis has played an important role in watermelon production, yet hybrid seed production in most countries still follow a complicated procedure of emasculating, bagging, and pollinating by hand. The procedure is troublesome and time-consuming and it is difficult to guarantee the purity of watermelon hybrid seeds. The use of male-sterility is the best way to solve the problem. Since Watts Ž1962. first obtained a male-sterile watermelon by irradiation, much attention has been paid to the use of male-sterility. Xia et al. Ž1988. found a naturally occurring male-sterile watermelon Abbreviations: DMSW, dwarf, male-sterile watermelon; MFPs, male fertile plants; MSPs, male-sterile plants; HMFPs, heterozygotic male-fertile plants ) Corresponding author. Tel.: q86 20 87596508; fax: q86 20 87503358. 0304-4238r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 4 2 3 8 Ž 9 7 . 0 0 1 0 2 - 7
176
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
mutant which Liu et al. Ž1991. used in their breeding programme and varieties developed by them have now been released. In 1989, the authors discovered a naturally occurring dwarf, male-sterile mutant in an introduced watermelon population. The use of this dwarf, male-sterile watermelon should simplify the production of hybrid seeds and thus, lower its cost. In this report, we investigated male-sterility, its mechanism and the dwarf gene of the dwarf, male-sterile watermelon.
2. Materials and methods 2.1. InÕestigation of the male-sterile gene and its genetic pattern In test 1, the dwarf, male-sterile watermelon ŽDMSW. was crossed with three cultivars, namely ‘Changhui’, ‘Fuyandagua’ and ‘America B’, and the fertility of the offspring in the F1 and F2 generations was investigated. In test 2, the pollen of male-fertile plants ŽMFPs. was used to fertilize pistillate flowers of male-sterile plants ŽMSPs. of the same plant line; the fertility of the offspring was also investigated. 2.2. InÕestigation of the dwarf gene The DMSW was crossed with ‘Sugar Bush’ and ‘Xinjiang Dwarf Watermelon’, and the height of the offspring in the F1 and F2 generations was investigated. 2.3. Breeding of a dual-purpose line Pollen of heterozygotic male-fertile plants ŽHMFPs. was used to pollinate pistillate flowers of MSPs of the same plant line, and seeds from the MSPs were collected. The offspring obtained were 50% HMFPs and 50% MSPs. This dual-purpose line can, therefore, propagate and maintain the male-sterile line by repeatedly crossing MSPs with HMFPs of the same plant line. 2.4. Cytological studies Staminate buds at different development stages were picked from HMFPs and MSPs of the dual-purpose line and immediately fixed in Carnoy fixative. Microspore development was investigated by the smearing technique using acetocarmine as staining agent. The structure of the anthers was investigated by paraffin microtomy using safranine as staining agent. 2.5. Chromosome obserÕations Young leaves of HMFPs and MSPs of the dual-purpose line were taken, fixed in Carnoy fixative and treated with a mixed enzyme solution of 3.0% cellulase and 2.5%
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
177
pectinase for 2 h at 258C. The treated leaves were smeared and chromosomes were counted under a microscope using acetocarmine as staining agent.
3. Results 3.1. Study of male-sterility DMSW plants differ greatly in morphology from normal plants ŽFig. 1.. DMSW is about 1.5-m tall with fewer leaf lobes Žfewer lobes leaf is between normal leaf and non-lobes leaf. than normal plants and could readily be identified by its leaf characteristics when 2–3 true leaves were present. Bud size of the DMSW only varied a little at different development stages. Most of the staminate flowers did not open. Of the staminate flowers that did open, most of the anthers were greenish yellow or brown. It seemed that the development of the male organs had been somehow stunted. To make use of male-sterility, it is imperative to know its genetic pattern. Table 1 shows that the ratio of MFPs and MSPs in the F2 generation in all three combinations conformed to a 3:1 segregation rate. Table 2 shows that the ratio of HMFPs and MSPs in the offspring of backcrosses conformed to a 1:1 segregation rate, from which it could be inferred that male-sterility of DMSW is controlled by a pair of recessive nuclear genes. Because of the simultaneous appearance of male-sterility and dwarfism, we name the male-sterile gene as ms d w , its genetic model is as Figs. 2 and 3. Observations of on anthers at different developmental stages from MSPs showed that the development of male-sterility differed among individual plants. Tetrads of some
Fig. 1. Comparison of DMSW Žright. and normal plants Žleft..
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
178
Table 1 Fertility segregation in the F2 generation Combinations
Number of plants
DMSW=‘Changhui’ DMSW=‘Fuyandagua’ DMSW=‘America B’
In total
Male-fertile
Male-sterile
103 104 63
75 78 44
28 26 19
Male-fertile:male-sterile
X 2 value
2.7:1 3:1 2.3:1
0.1586 0.0128 0.6402
2 X 005.1 s 3.84.
anthers congregated in the tetrad stage and failed to develop into normal pollen grains; while other anthers developed normally until the mid-monokaryon stage, and then the pollen began to wrinkle and was aborted. No matter when pollen abortion took place, no pollen grains or only a few empty pollen grains were present in the anther chambers when the flowers bloomed and the pollen was completely aborted. Observations of the structure of the anthers of MSPs by paraffin microtomy showed that there was abnormal partial increment of tapetum which was one of the reasons that made pollen abort early because the microspores were squeezed. This did not occur in the anthers of MFPs. Because of the similarity between seeds of the MSPs and multiploids, the chromosomes of MSPs were examined to see if male-sterility was caused by a change in chromosome number. The results showed that MSPs had the normal number of chromosomes ŽTable 3.. 3.2. Study of the dwarf gene of DMSW So far, three dwarf genes of watermelon Ž dw-1, dw-1s, dw-2 . have been reported; dw-1 and dw-1s are allelic while dw-1 and dw-2 are non-allelic ŽLin, 1992.. In one of our tests, DMSW was crossed with normal plants and all plants in the F1 generation were normal, while the ratio of normal to dwarf plants in the F2 generation conformed to a 3:1 segregation ratio. In another test, DMSW was crossed with both ‘Sugar Bush’ Ž dw-1dw-1. and ‘Xinjiang Dwarf Watermelon’ Ž dw-2dw-2 .. All the plants in the F1 were normal, while in the F2 , there were dwarf plants and DMSW in addition to normal plants. When some dwarf plants were self-fed, DMSW appeared in the offspring, while in the offspring of cross between some DMSW and dwarf plants in the same plant line, only DMSW and dwarf plants appeared. From these results, it could be inferred that
Table 2 Fertility segregation in the offspring of a backcross Combinations
DMSW=HMFP1 DMSW=HMFP2 2 X 0.05.1 s 3.84
Number of plants In total
Male-fertile
Male-sterile
15 11
8 6
7 5
Male-fertile:male-sterile
X 2 value
1.1:1 1.2:1
0 0
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
179
Fig. 2. Fertility gene segregation in the F2 generation.
there is a new dwarf gene Ž dw-3 . in watermelon in addition to three reported dwarf genes. This dwarf gene appears simultaneously with male-sterility and its expression seems to be concealed by dw-1 and dw-2. The relationship among four dwarf genes needs further investigation. 3.3. Breeding of dual-purpose line Generally, a two-line method is adopted in order to make use of nuclear male-sterility. Excellent multi-typic dual-purpose line is the basis of application. Cross MSPs with watermelon material of good agricultural characteristics and screen the plant lines whose offspring show 1:1 ratio of HMFPs and MSPs. In such a plant line, sister cross between MSPs and HMFPs is made. With such cycling cross and selection, stable dual-purpose line can be obtained. So far, four types of male-sterile line have been developed by such methods: Ža. light green rind, elongate fruit, male-sterile line; Žb. black rind, round fruit, male-sterile line; Žc. dotted rind, round fruit, male-sterile line; Žd. light green rind, round fruit, male-sterile line. Because the original MSPs had fewer seeds per fruit Ž50–100 seeds per fruit. than normal fertile plants, the problem of how to increase the number of seeds per fruit of MSPs is also one of the objective of breeding the dual-purpose line. Improved MSPs with more seeds per fruit have been obtained to some extent, with the highest number of seeds per fruit being 360. Our experiments showed that selection of
Fig. 3. Fertility gene segregation in the offspring of a backcross.
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
180
Table 3 Comparison of chromosome numbers in MSPs and HMFPs Plant type
Number of cells with 22 chromosomes 44 chromosomes
Other numbers of chromosomes
Percentage of cells with 22 chromosomes
MSPs HMFPs
22 30
0 0
100 96.9
0 1
watermelon materials with a high number of seeds per fruit as a parent was an effective way to improve the number of seeds per fruit of MSPs.
4. Discussion So far, several male-sterile watermelon have been reported. Because it is not necessary to match three-line combinations and a potent recovery line is easy to obtain, application of watermelon male-sterility has become hot topic of watermelon breeding and is getting more and more attention. How to maintain male-sterile line and identify MSPs in a mixed population in early stages should be solved before male-sterility can be used in breeding programmes. In DMSW, male-sterility appears simultaneously with dwarfism and fewer leaf lobes. Dwarfism makes it possible to increase planting density
Fig. 4. Model for maintaining the male-sterile line and hybrid seed production with a dual purpose line.
H. Hexun et al.r Scientia Horticulturae 74 (1998) 175–181
181
and thus, to increase seed production per unit area. Fewer leaf lobes is a marker. So, DMSW is a very valuable male-sterile material. In order to make use of DMSW, two-line methods can be adopted, i.e. select a stable dual-purpose line which shows 1:1 ratio of MSPs and HMFPs in the offspring population. The dual-purpose line can propagate and maintain the male-sterile line. When dual-purpose line is used to maintain the male-sterile line, pollen of HMFPs is used to pollinate stigmas of MSPs in the same dual-purpose line, seeds in MSPs are collected and its offsprings will still show 1:1 ratio of MSPs and HMFPs. When dual-purpose line is to be used in the hybrid seed production, the planting density is doubled, and HMFPs are eradicated in the seedling stage according to leaf characteristics, the remaining plants are MSPs. When MSPs are planted with recovery line alternately, pollen of recovery line will pollinate the stigmas of MSPs. Seeds collected from MSPs can be used in watermelon production. This seed-production method gets rid of the troublesome procedure of emasculating, bagging, and pollinating by hand. Its maintaining and seed-production model is as Fig. 4. If a diheterozygotic maintaining line can be developed using chromosome translocation techniques ŽPatterson, 1973., application of DMSW would be more effective.
References Lin, D.P., 1992. Gene directory of watermelon Ž1991. Žin Chinese.. Translated from CGC report ŽAugust 1991.. China Watermelon and Muskmelon, 2, pp. 1–4. Liu, Y.A., Chen, A.B., Wu, X.L., 1991. Application of male-sterile dual-purpose line of watermelon G17AB. China Watermelon Muskmelon 2, 6–10, in Chinese. Patterson, E.B., 1973. Proc. 7th Meeting Maize and Sorghum Seet. Eucarpia, Sept. 3–6. Zagreb, Yugoslavia. Watts, V.M., 1962. A marked male-sterile mutant in watermelon. Proc. Am. Soc. Hort. Sci. 81, 498–505. Xia, X.T., Liu, Y.A., Liu, E.J., Chen, A.B., 1988. Selection of dual-purpose male-sterile line of G17AB watermelon. J. Shenyang Agric. Univ. 19 Ž1., 9–13, in Chinese.