61 1. Introduction Juglans regia plants are monoecious, anemophilous with unisexual flowers grouped in separate inflorescenc- es (Manning, 1938; Bauckmann, 1974; Germain et al., 1981). Staminate flowers (catkins) develop from lateral buds in the axil of leaves on the previous season’s growth. Pistillate flowers are borne terminally on the current sea- son’s growth, however in some cultivars, also develops in a lateral position on the last year’s growth (Forde, 1977). Although Juglans regia cultivars are self fertile, but low yields in walnut is a cause of concern which is mainly attributed to inadequate pollination resulting from pistil- late flower abscission (PFA) and adverse climatic con- ditions during pollen shedding and stigma receptivity. Apart from these factors, dichogamy is also a main cause for low yields in walnut which was steady and biological characteristics of walnut (Akca and Sen, 1997). The phenomenon of dichogamy involves development on the same plant of male and female organs at differ- ent times. ‘Protandry’ refers to the shedding of pollen prior to stigma receptivity and ‘protogyny’ the reverse sequence (Gleeson, 1982). The mating system with both protandrous and protogynous plants within the species has been classified as heterodichogamy (Gleeson, 1982; Luza and Polito, 1988). The extent of heterodichogamy varies from almost complete overlap (homogamy) to complete separation of male and female bloom periods (McGranahan and Leslie, 1991). The degree and nature of dichogamy is a varietal character, but it is also greatly affected by the age of the tree, climate and geographic location (Wood, 1932). Walnut variety or locality is free from dichogamy. On the basis of these data it is possible to make combinations of cultivars, which ensure pollinat- ing and enable regular harvest. The present work deals with protandrous-protogynous dimorphism in 20 walnut cultivars/selections. To overcome the problem of low yields and to identify suitable cultivars that can overlap in blooming time, the present study was conducted at the University of Horticulture and Forestry, Nauni-Solan for three consecutive years. On this basis we can define the most suitable combinations of cultivars for north-western region of India. Protandrous-protogynous dimorphism in indigenous selections from North Western India and some exotic cultivars of Persian walnut (Juglans regia L.) A. Kumar*, N. Sharma** * Division of Fruit Science, Sher-e-Kashmir University Agricultural Sciences and Technology, Kash- mir, Shalimar, Srinagar, Jammu and Kashmir, India. ** Division of Fruit Science, Sher-e-Kashmire University Agricoltural Sciences and Tecnology, Jammu, Chatta, Jammu, Jammy and Kashmir, India. Key words: dichogamy, low productivity, pollen shedding, stigma receptivity, walnut. Abstract: Walnut (Juglans regia L.) is one of the most important temperate nuts grown worldwide. In India, however, most of the produce comes from age-old trees of unknown origin. Apart from non-adoption of standard farm practices, certain in- herent problems like dichogamy are the major factors of low productivity. The problem of dichogamy is further aggravated by short period of pollen shedding and stigma receptivity. Dichogamy in walnut prevents self-pollination and necessitates cross-pollination to set fruits. For optimum fruit set and consequent yield, an attempt was made with 20 cultivars/selections grafted on seedling walnuts for three consecutive years to determine the nature and degree of dichogamy. Observations were recorded on the time of male and female flowering, duration of pollen shedding and stigma receptivity, nature and degree of dichogamy. Results indicate that out of 20 cultivars/selections fourteen have protandrous nature, ‘Gobind’ in the first and third year, ‘KX Giant’ in second and third year and ‘Plant No. 45’ in the second year have homogamous nature and only ‘Gobind’ have protogynous nature in the second year. Degree of dichogamy varies from zero to 100 per cent among various cultivars/selections. Findings of the present study emphasized on the interplanting of protandrous and protogynous cultivars or homogamous cultivars to ensure adequate pollination to obtain higher nut yields in walnut. Adv. Hort. Sci., 2013 27(1-2): 61-66 Received for publication 20 March 2013 Accepted for publication 24 April 2013 62 2. Materials and Methods The present study was carried out over a three-year period (2006-2008) in the walnut germplasm collection block of the Department of Fruit Breeding and Genetic Resources, Dr. Y S Parmar University of Horticulture and Forestry, Nauni-Solan, Himachal Pradesh. The wal- nut block is located at an elevation of 1225 m a.m.s.l. and between 31oN latitude and 77oE longitude. The mean av- erage rainfall of the study area during the flowering sea- son (February to April) ranges from 125 to 200 mm. The minimum and maximum temperatures of the field area during the flowering season range between 10 and 30oC. The experiment was conducted with the following 20 cul- tivars/selections: ‘ACO 38853’, ‘Blackmore’, ‘Gobind’, ‘Hartley’, ‘Plant No.10’, ‘Netar Akhrot’, ‘Roopa Akhrot’, ‘KX Giant’, ‘Rattan Akhrot’, ‘Lake English’, ‘Kandaghat Selection’, ‘Payne’, ‘Inder Akhrot’, ‘Plant No. 32’, ‘Xe- nia’, ‘Plant No. 45’, ‘Plant No. 46’, ‘Plant No. 47’, ‘Sold- ing Selection’ and ‘Luxmi Akhrot’. These cultivars/selec- tions were grafted on walnut seedlings and the age of the planting material during the study was 18-20 years old. The grafted plants were planted at a distance of 7x7 m and standard practices of orchard management were followed. Observations were taken with regard to time of male and female flowering, duration of pollen shedding and stigma receptivity, nature and degree of dichogamy. Nature of di- chogamy was determined as Protandry: Maturation of male catkins prior to stigma receptivity of female flower Protogyny: Stigma receptivity prior to maturation of male catkins Homogamy: Maturation of male catkins coinciding with stigma receptivity in female flowers. Degree of dichogamy was calculated according to the formula suggested by Solar et al. (1997). Degree of dichogamy (%) = = 1 - No. of days when male and female flowering coincides X 100 Number of days of female flowering 3. Results and Discussion The results obtained from the three consecutive years of study showed variation with respect to time of male and female flowering, duration of pollen shedding and stigma receptivity, nature and degree of dichogamy. The earliest emergence of catkins in all three years was recorded in ‘Plant No. 45’ (i.e. 12 March, 17 March and 15 March in the first, second and third years, respectively) along with ‘Luxmi Akhrot’ (12 March) in the first year, and ‘Netar Akhrot’ and ‘Inder Akhrot’ (17 March) in the second year (Fig. 1). Late emergence of catkins was observed in ‘Sold- ing Selection’ (25 March) in the first year; in the second and third years late emergence was observed in ‘Gobind’ (7 April and 28 March, respectively). ‘Plant No. 45’ showed early female flowering (15 March in the first year, 22 March in second and 17 March in the third), whereas late emergence of female flowering in the first year was observed in ‘Rattan Akhrot’ (31 March), in the second year in ‘Plant No. 32’ (8 April) and in the third in ‘ACO 38853’ and ‘Luxmi Akhrot’ (1 April). Early pollen shedding in 2006 and 2008 was recorded in ‘Plant No. 45’ (17 March and 20 March, respectively) along with ‘Hartley’ and ‘Luxmi Akhrot’ in 2006, howev- er, it was recorded in ‘Netar Akhrot’ in 2007 (24 March) (Fig. 2). As for late pollen shedding the following obser- vations were made: ‘Solding Selection’ (30 March 2006) and ‘Gobind’ (10 April 2007 and 1 April 2008). In all three years ‘Plant No. 45’ had early stigma receptivity (19 March, 25 March and 21 March, respectively). However, there was late stigma receptivity in ‘Rattan Akhrot’ in the first year (5 April), ‘Plant No. 32’ and ‘Xenia’ in the sec- ond year (12 April) and ‘ACO 38853’, ‘Blackmore’ and ‘Luxmi Akhrot’ in the third year (5 April). Regarding the nature of dichogamy, it is clear from Table 1 that ‘Gobind’ was found to be homogamous in the first and third years, ‘KX Giant’ in the second and third years and ‘Plant No. 45’ in the second year. However, dur- ing the study period only ‘Gobind’ showed a protogynous nature in the second year. While ‘KX Giant’, ‘Plant No. 32’ and ‘Plant No. 45’ in 2006, ‘Netar Akhrot’ and ‘Xe- nia’ in 2007 and again ‘Plant No. 45’ in 2008 revealed a slight protandrous nature. All the other cultivars were of protandrous nature in all years. ‘ACO 38853’, ‘Black- more’, ‘Hartley’, ‘Roopa Akhrot’, ‘Lake English’, ‘Inder Akhrot’, ‘Plant No. 47’ and ‘Luxmi Akhrot’ were found to have a 100% degree of dichogamy during the course of study; ‘KX Giant’ and ‘Plant No. 45’ in the second year, and ‘Gobind’ in the third year showed a 0% degree of di- chogamy. Other cultivars/selections had a wide range of degrees of dichogamy during the study. From the present study it is clear that Persian walnut has a large variation with regard to nature and degree of dichogamy. The degree of dichogamy in various cultivars/ selections varies from zero to 100%. It is generally as- sumed that protandrous cultivars are the most numerous, followed by protogynous types, while homogamous types are quite rare (McDaniel, 1957; Majackaja, 1969; Ger- main et al., 1981) as also revealed in the present study. The trend here is towards protandry with as many as fourteen protandrous cultivars/selections (‘ACO 38853’, ‘Black- more’, ‘Hartley’, ‘Plant No. 10’, ‘Roopa Akhrot’, ‘Rattan Akhrot’, ‘Lake English’, ‘Kandaghat Selection’, ‘Payne’, ‘Inder Akhrot’, ‘Plant No. 46’, ‘Plant No. 47’, ‘Solding Selection’ and ‘Luxmi Akhrot’) as demonstrated from the extent of synchronization of male and female flowering, and especially the time of pollen shedding and stigma re- ceptivity. ‘Gobind’ in the first and third years, ‘KX Gi- ant’ in second and third and ‘Plant No. 45’ in the second year had a homogamous nature, whereas only ‘Gobind’ showed a protogynous nature in the second year. How- ever, the trend towards protandry was also reported by earlier researchers. Germain et al. (1983 a) found among 63 64 65 Table 1 - Nature and degree of dichogamy in different walnut cultivars/selections Cultivar/selection First year Second year Third year Nature Degree Nature Degree Nature Degree ACO 38853 Protandrous 100 Protandrous 100 Protandrous 100 Blackmore Protandrous 100 Protandrous 100 Protandrous 100 Gobind Homogamous 14.28 Protogynous 50 Homogamous 0 Hartley Protandrous 100 Protandrous 100 Protandrous 100 Plant No. 10 Protandrous 100 Protandrous 83.33 Protandrous 83.33 Netar Akhrot Protandrous 62.50 Slightly protandry 33.33 Protandrous 57.14 Roopa Akhrot Protandrous 100 Protandrous 100 Protandrous 100 KX Giant Slightly protandry 33.33 Homogamous 0 Homogamous 14.28 Rattan Akhrot Protandrous 100 Protandrous 60 Protandrous 57.14 Lake English Protandrous 100 Protandrous 100 Protandrous 100 Kandaghat Selection Protandrous 71.43 Protandrous 100 Protandrous 100 Payne Protandrous 80 Protandrous 60 Protandrous 50 Inder Akhrot Protandrous 100 Protandrous 100 Protandrous 100 Plant No. 32 Slightly protandry 28.57 Protandrous 100 Protandrous 42.86 Xenia Protandrous 83.33 Slightly protandry 33.33 Protandrous 50 Plant No. 45 Slightly protandry 16.67 Homogamous 0 Slightly protandry 14.28 Plant No. 46 Protandrous 66.67 Protandrous 100 Protandrous 71.42 Plant No. 47 Protandrous 100 Protandrous 100 Protandrous 100 Solding Selection Protandrous 42.86 Protandrous 60 Protandrous 42.86 Luxmi Akhrot Protandrous 100 Protandrous 100 Protandrous 100 20 French cultivars 16 protandrous, three protogynous and one homogamous. Among 100 cultivars studied by Yadrov (1982) the majority was protandrous (approximately 60%), while approximately 30% were protogynous and only 10 % were homogamous. Working on 10 cultivars of French and American origin Aleta and Ninot (1987) identified six ab- solutely protandrous cultivars, one protogynous and three partly homogamous. Korac et al. (1989) found among 14 cultivars, 11 protandrous, two protogynous and one partly homogamous. The occurrence of heterodichogamy in Per- sian walnut (i.e. protandry, protogyny and homogamy) as revealed here, is reported also by several other workers (Cheng, 1978; Radicati, et al., 1983; Cerovic et al., 1995). The present investigation on the nature of dichogamy is primarily based upon the overlap between pollen shedding and stigma receptivity and not on the conventional method of classifying varieties on the basis of time of emergence of male and female flowers. The degree and nature of dichog- amy is a varietal character, but it is also greatly affected by tree age, climate and geographic location (Wood, 1932). Thus it is concluded that dichogamy is genotype-spe- cific as shown from the considerable variation observed in the 20 cultivars/selections studied. To achieve optimum fruit set and consequent yield, near homogamous types (‘Gobind’ or ‘KX Giant’) may be planted in single cultivar walnut orchards, or a mixture of cultivars can be interplant- ed to allow sufficient overlap between pollen shedding and stigma receptivity. On the basis of the present study on pro- tandrous-protogynous dimorphism, the mentioned possible pollinators in Table 2 are suggested as suitable cultivars/ selections for growing in north-western India. References AKCA Y., SEN S.M., 1997 - The relationship between dichog- amy and yield-nut characteristics in Juglans regia L. - Acta Horticulturae, 442: 215-216. ALETA N., NINOT A., 1987 - El Nogal. Un cultivo tradicional con futuro. - Fruticultura professional, 11: 55-59. BAUCKMANN M., 1974 - The length of male flowers (cat- kins) on grafted walnut trees. - Mitt. Rebe Wein, Obstbau Freuchterwert, 24: 463-466. CEROVIC S., KORAC M., TODOROVIC J.N., 1995 - Dichoga- my in walnut (Juglans regia L.). - Jugoslovensko Vocarstvo, 29(3/4): 21-25. CHENG W.C., 1978 - Juglans Regia L. - The Editorial Commis- sion of Chinese Flora of Trees. The planting technology of the main forest trees in China, pp. 1342. FORDE H.I., 1977 - Walnuts, pp. 439-455. - In: JANICK J. and J.N. MOORE (eds.). Advances in fruit breeding. Purdue Uni- versity Press, West Lafayette Ind., USA. GERMAIN E., JALINAT J., MARCHOU M., 1981 - Divers as- pects de la biologie florale de noyer, pp. 13-27. - In: BER- GOUGNOUX F., and P. GROSPIERRE(eds.) Le Noyer. IN- VUFLEC, Paris France. GERMAIN E., JALINAT J., LEGLISE P., MASSERON A., TRONEL C., CHARTIER A., 1983 a - Le noyer, resultants de 20 ans experimentation. - Arb. Fruit., 356: 55-60. 66 GLEESON S.K., 1982 - Heterodichogamy in walnuts. Inheri- tance and stable ratios. - Evolution, 36(5): 892-902. KORAC M., CEROVIC S., MITROVIAC M., KUZMANOVS- KI I., JOVANEEVIAC D., SOLAR A., 1989- Walnut produc- tion, population variability and breeding results achieved in Yugoslavia. First Int. Symp. on Walnut Production, Buda- pest, Hungary, 25-29 Sept., pp. 9. LUZA J.G., POLITO V.S., 1988 - Microsporogenesis and anther differentiation in Juglans regia L.; a developmental basis for heterodichogamy in walnut. - Bot. Gaz., 149(1): 30-36. MAJACKAJA A.D., 1969 - Dichogamy and fruiting in walnuts. - Lesn. Hoz., 2: 32-35. MANNING W.E., 1938 - The morphology of the flowers of Juglandaceae. I. The inflorescence. - American Journal of Botany, 25: 407-419. McDANIEL J.C., 1957 - The pollination of Juglandaceae vari- eties – Illinois observations and review of earlier studies. - Nut Growers Assn. Annual Rep., 48: 89-93. McGRANAHAN G.H., LESLIE C., 1991 - Walnuts (Jug- lans), pp. 907-951. - In: BALLINGTON J.R., and J.N. MOORE(eds.) Genetic resources of temperate fruit and nut crops. ISHS Secretariat, The Netherlands, Vol. II, pp. 980. RADICATI L., ME G., SACERDOTE S., VALLANIA R., 1983 - Prime valutazioni di cultivars di noci Americana e francesi per le zone Montana. - Frutticoltura, 45(3-4): 19-23. SOLAR S., STAMPER F., SMOLE J., 1997 - The degree of het- erodichogamy of some walnut cultivars (Juglans regia L.) in Slovenia. - Acta Horticulturae, 442: 217-224. WOOD M.N., 1932 - Dichogamy- An important factor affecting production in the Persian walnut. - Proceedings of American Society for Horticultural Science, 34: 160-164. YADROV, A.A. 1982. Dichogamy and fruit production in wal- nut. - Byulleten Gosudarstvennogo Nikitskogo Botanichesk- ogo Sada, 49: 68-72. Table 2 - Suitable pollinators for different walnut cultivars/selections Main cultivars/selections Suitable pollinators ACO 38853 Plant No. 32 Blackmore Gobind, Xenia Gobind Xenia, Plant No. 32 Hartley Gobind, Xenia, Plant No. 32 Plant No. 10 Gobind, Xenia, Plant No. 32 Netar Akhrot Roopa Akhrot, Inder Akhrot, Plant No. 45, Lake English Roopa Akhrot KX Giant, Plant No. 32, Plant No. 46 KX Giant Kandaghat Selection, Plant No. 10 Rattan Akhrot Plant No. 32, Plant No. 46 Kandaghat Selection Plant No. 32, Xenia Payne Plant No. 32, Xenia Inder Akhrot Plant No. 32, KX Giant, Solding Selection Plant No. 32 Gobind Xenia Gobind Plant No. 45 Roopa Akhrot, Netar Akhrot Plant No. 46 Gobind, Xenia Plant No. 47 Solding Selection, Gobind, ACO 38853 Solding Selection Plant No. 32, KX Giant Luxmi Akhrot Plant No. 32, Solding Selection, KX Giant, ACO 38853