Trait-specific accessions in global castor (Ricinus communis L.) germplasm core set for utilization in castor improvement

Industrial Crops & Products 112 (2018) 766–774

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Trait-specific accessions in global castor (Ricinus communis L.) germplasm core set for utilization in castor improvement

T

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K. Anjania, , M.A. Raoofa, M. Santha Lakshmi Prasada, P. Duraimurugana, C. Lucoseb, Praduman Yadava, R.D. Prasada, J. Jawahar Lala, C. Saradaa a b

ICAR-Indian Institute of Oilseeds Research, Hyderabad, 500030, India Main Oilseeds Research Station, Junagadh Agricultural University, Junagadh, Gujarat, India

A R T I C L E I N F O

A B S T R A C T

Keywords: Biotic stress Castor Core set Germplasm Resistance Ricinoleic acid

Castor (Ricinus communis L.) is a non-edible industrial oilseed crop. Its oil has multiferous applications in industry. A vast castor germplasm collection of 3289 accessions is being maintained at ICAR-Indian Institute of Oilseeds Research, Hyderabad, India. The large size of castor germplasm has become a problem for evaluation, conservation and utilization. Hence, a core-set comprising 165 accessions representing diversity in the entire collection was developed. Though the core set is genetically diverse, its utilization in breeding programme is not picking up because of its still large size. In order to enhance efficacy of core set, an attempt was made in to identify core set accessions possessing resistance to major biotic stresses such as Fusarium wilt, root rot, gray mold and leafhopper, and desirable qualitative and quantitative traits. Screening against biotic stresses was done under artificial infestation conditions in field and greenhouse/ploy house at multilocations over years. Evaluation for stability of quantitative and qualitative traits was done at multilocations under rainfed and irrigated conditions. This study has thus identified 26 core set accessions possessing resistance to wilt, root rot, gray mold and leafhopper, and high ricinoleic acid content, high yield and seed weight and early maturity. These accessions would serve as instant basic resources for utilization in breeding programmes to improve castor for resistance to major biotic stresses as well for yield, ricinoleic acid content and early maturity. They also play an important role in diversifying the genetic base of working collection of castor breeders for developing improved cultivars with broad genetic base.

1. Introduction Castor (Ricinus communis L.) is an important industrial oilseed crop grown in marginal lands. Its oil is used in production of wide range of industrial products such as biopolymers, aviation fuel, medicines etc. (Ogunniyi, 2006). The potential for castor oil to play a much larger role in the world economy had increased dramatically. India is the largest producer of castor and secured a virtual monopoly in castor production with 1751 thousand tones production from 1061 thousand ha area with 1652 kg/ha productivity in 2015–16. Mozambique, China and Brazil are the other major castor producing countries (http://www.fao.org/ faostat/). India is considered as one of the centres of origin of castor because of existence of vast diversity in this species. The Indian Council of Agricultural Research-Indian Institute of Oilseeds Research (ICARIIOR), Hyderabad, India is the prime castor research centre in India. It currently holds around 3289 castor germplasm accessions, of which 3036 were collected through conduction of explorations in India

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(Anjani, 2012), and 253 accessions were introduced from 36 countries. However, conservation and maintenance of genetic purity of this vast global collection is expensive and labour intensive owing to prolonged indeterminate growth habit of castor plant. Castor is a cross-pollinating plant; wind is the main pollinating agent. Hence, production of large quantity of self-seed of each accession is a labour intensive and laborious task. The large size of germplasm collection is posing problems for multilocation evaluation. Enormous efforts are needed to evaluate the entire collection for traits of economic importance and to screen against biotic and abiotic stresses through reliable standardized techniques. This is a very expensive and time taking task. Therefore, there is lack of information on genotype x environment interaction of germplasm collections whose performance is often environment dependent. Consequently, the potentiality of germplasm is not being exploited fully by breeders; breeders tend to utilize the same in-house breeding pools in crop improvement programmes which results into utilization of the same genotypes repeatedly, and hence, narrow genetic base of breeding

Corresponding author. E-mail address: [email protected] (K. Anjani).

https://doi.org/10.1016/j.indcrop.2018.01.002 Received 16 September 2017; Received in revised form 1 December 2017; Accepted 3 January 2018 0926-6690/ © 2018 Elsevier B.V. All rights reserved.

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germination and wilt incidence at 30 days interval up to 150 days after sowing were recorded. The data on total plant count and infected plants were recorded. Wilt incidence was derived from the formula: [(number of wilted plants/total number of plants) x 100]. Number of wilted plants were recorded at different intervals. At each interval, the newly wilted plants were counted leaving the previously infected ones; finally the wilted plants counted at each interval were cumulated to calculate wilt incidence of each genotype. Reaction of experimental material against wilt was categorized as per the scale given by Lakshminarayana and Raoof (2006). Based on the wilt incidence, the genotypes found free from wilt disease (0% wilt disease) were regarded as highly resistant. The cultivars with wilt incidence up to 20% were classified as resistant and those with more than 20% wilt incidence were considered as susceptible. Germplasm accessions showing resistant reaction in wilt sick plot at three locations were reconfirmed by root-dip inoculation method (Raoof and Nageshwar Rao, 1996) in greenhouse at ICAR-IIOR, Hyderabad and S.K. Nagar.

lines and released cultivars. In order to overcome these problems, a castor germplasm core set was developed from the entire collection of 3003 accessions available at that time at ICAR-IIOR (Sarada and Anjani, 2013). The core set is comprised of 165 accessions and represents the diversity present in the entire collection, and displayed excellent diversity for agro-morphological traits. Prior to establishing the core set each accession has undergone 7–8 generations of self-pollination and thus genetic uniformity was maintained in each accession. Senthilvel et al. (2016) showed low level of genetic relatedness and absence of population structure among the germplasm accessions comprising core set. This indicates presence of great genetic diversity in castor core set. The difficulties involved in utilization of vast collection of germplasm in castor breeding programmes for enhancing genetic variation, and the low productivity of castor due to biotic stresses has necessitated the germplasm curators to identify sources of resistance to biotic stresses as well accessions possessing desirable economic and quality traits in the castor core set as it represents the diversity present in the entire collection. Hence, the main objective of this study was to identify trait-specific accessions in castor core set so as to further enhance efficiency of core set in breeding programmes to develop new high yielding cultivars with a broad genetic base. Castor productivity is adversely affected by several biotic stresses. Fusarium wilt [Fusarium oxysporum f.sp. ricini (Nanda and Prasad)], Macrophomina root rot [Macrophomina phaseolina (Tassi) Goid], gray mold [Botryotinia ricini (Godfrey) Whetzel] and leafhopper [Empoasca flavescens (F.)] are some of the major biotic stresses in castor and can cause more than 80% yield loss (Anjani et al., 2004). Since host plant resistance is the major component in the management of diseases and insect pests in castor, the accessions comprising core set were screened along with other accessions against major biotic stresses such as Fusarium wilt, Macrophomina root rot, gray mold and leafhopper at different locations under artificial infestation conditions in different years. In addition, the promising accessions identified based on first year evaluation for economic and phenological traits at two locations were later evaluated at four locations under rainfed and irrigated conditions. The screening and evaluation results are discussed in the present paper in order to increase the efficacy of core collection in castor improvement programmes.

2.1.2. Root-dip inoculation method The surface sterilized seeds of each germplasm accession were sown in autoclaved sand filled with plastic trays. The trays are watered as and when needed. F. oxysporum f. sp. ricini was isolated from naturally wilt infected castor roots on potato dextrose agar medium. The pure culture of fungus was grown on sterilized sorghum grains for 10-14 days. The spore suspension was prepared by transferring a few infected sorghum grains into distilled water to maintain concentration of 1 × 106 spores/ ml. Ten days old seedlings of individual accession were carefully uprooted, washed thoroughly with tap water and, then the clipped root tips were dipped for 1–2 min in the spore suspension. Inoculated seedlings were transplanted in the earthen pots filled with autoclaved soil; twenty seedlings were maintained for each accession. The resistant and susceptible checks were screened along with the test material. Suitable controls were maintained by dipping the trimmed seedlings in sterile distilled water and transplanted into the pots. The plants were observed for wilt symptoms and observations on wilt incidence were recorded periodically up to 30 days after transplanting. 2.2. Screening against root rot

2. Material and methods 2.2.1. Root rot sick plot The 165 accessions of core set were screened along with other germplasm accessions against root rot in a permanent root rot sick plot at Main Oilseeds Research Station, Junagadh Agricultural University, Junagadh, India (21.31°N and 70.33°E). The accessions of core set were screened separately over years from 2003-04 to 2015–16. Screening of germplasm accessions against root rot was done initially in the permanent root rot sick plot along with susceptible check, GCH-4 and resistant check, JI-357 planted after every five test rows at 90 × 45 cm spacing. GCH-4 is a commercial castor hybrid and JI-357 is an inbred line. The root rot pathogen, M. phaseolina, was isolated from naturally infected castor plants and grown on sorghum sand medium for 14 days. The sorghum culture mixed with sand was applied in furrows at the time of sowing. The experimental materials were categorized as per Mayee and Datar (1986). The germination percentage and root rot incidence at 120, 150 and 180 days after sowing were recorded. The ratio of number of root rot infected plants to total number of plants multiplied by 100 was considered as root rot incidence percentage. Number of plants infected by root rot at different intervals were recorded. At each interval, the newly infected plants were counted leaving the previously infected ones; finally the root rot infected plants counted at each interval were cumulated to calculate root rot incidence of each genotype.

2.1. Screening against wilt 2.1.1. Wilt sick plot The 165 accessions comprising the core set were screened against wilt (F. oxysporum f. sp. ricini) disease during rainy season in permanent wilt sick plots maintained at ICAR-IIOR, Hyderabad (17.366°N and 78.478°E), and S.K. Nagar (24.19°N and 72.19°E), an All India Coordinated Research Project (AICRP) on Castor centre. The core set accessions were screened separately over years (2001–2012) in sick plots. The susceptible check, JI-35/VP-1/Aruna/GAUCH-1 and the resistant check, 48-1/DCS-9 were sown after every five or 10 rows of test entries to determine the uniform spread of inoculum across the sick plot. All the checks used are commercial castor cultivars. Each test entry was sown in a single row of 5 m length with spacing of 60 × 30 cm. The permanent wilt sick plots at Hyderabad and S.K. Nagar were developed by growing highly susceptible variety, Aruna/VP1/JI35/GAUCH-1/Kranthi and also in situ incorporation of infected plant debris of susceptible varieties, and also inoculum was incorporated in wilt sick plots prior to sowing. Wilt pathogen, F. oxysporum f. sp. ricini was isolated from naturally infected wilted root and multiplied on sterilized sorghum grain medium for 14 days in bulk amount. The wilt infected sorghum grains were applied in furrows after 20 days of sowing. The inoculum load of F. oxysporum f. sp. ricini in soil was tested before and after sowing and also at the end of the trial by following standard soil dilution method. Inoculum load of 2–3 × 103 CFU/g of soil was being maintained in the sick plot. The observations on

2.2.2. Stem tape inoculation method The germplasm accessions which showed resistant reaction in root rot sick plot were evaluated against root rot by stem tape inoculation 767

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2.5. Analysis of fatty acid composition and oil content

method under pot culture conditions. Plants were maintained in pots containing sterilized soil under greenhouse conditions for 20 days. Twenty seedlings were maintained for each accession. The hypocotyl region of the test plants were superficially wounded by peeling the epidermis at 2–3 cm above the soil surface. Fresh mycelium bit of M. phaseolina of 4 mm in diameter with abundant sclerotia were used for inoculation and placed against the wound, covered it with cellophane tape. Control plants were inoculated with a sterile PDA disc. The inoculated plants were observed for root rot symptoms up to 20 days after inoculation. The percentage of dead plants and length of lesion on stems was recorded. The pots were watered daily to maintain the humidity in pots and the development of disease. The genotypes showing no root rot incidence were categorized as highly resistant and those having less than 20% root rot incidence as resistant.

Oil from the oven dried seeds was extracted in hexane on soxhlet apparatus. Fatty acid composition was determined using an Agilent 7890B gas chromatograph (California, USA) equipped with a flame ionization detector (FID) and an auto sampler as per the method of Yadav and Anjani (2017). The test materials were initially assayed for fatty acids at ICAR-IIOR, Hyderabad, and then the identified high ricinoleic acid type accessions were further evaluated at four locations under rainfed and irrigated conditions during 2014–16 in order to determine the stability of ricinoleic acid content. The locations under rainfed conditions were Hyderabad and Palem and under irrigated conditions were S.K. Nagar and Mandor. Oil content was analysed using a bench top pulsed low-resolution nuclear magnetic resonance analyser (Oxford-MQC-5, London, UK) according to the method of Yadav and Murthy (2016).

2.3. Screening against gray mold

2.6. Evaluation for economic and phenological traits

The core set germplasm accessions along with resistant (48-1) and susceptible (DCH-519, DCS-9) checks and other breeding lines were grown during rainy season inside poly house for screening against gray mold disease. DCH-519 is a commercial castor hybrid while 48-1, DCS-9 are varieties. Each test entry was sown in a single row of 6 m length with the spacing of 90 × 60 cm in augmented RBD with three replications. The checks were repeated after every three rows. The methodology proposed by Prasad et al. (2016) for screening against gray mold was followed. Favourable conditions for development of disease were maintained inside poly house by cooling pad and fan and fogging system. Around 25–28 °C temperature, 80–100% humidity and continuous wetness were maintained in poly house. Foggers on PVC lateral pipes were drawn above crop canopy to maintain wetness on castor spikes. Fogger system was operated for 10 min in every one hour during day time when plants were in 3–4 spike stage. Spore suspension of B. ricini (2 × 108 conidia/ml) prepared from 10-day-old culture was sprayed on spikes. Gray mold infection has developed on the spikes between 3 and 7 days after inoculation. As the experimental materials have varied in days to flowering, screening for host plant resistance was done based on artificial infection at right stage (before seed hardening) on spikes of identified plants using pictorial disease assessment key developed at ICAR-IIOR, Hyderabad (Prasad et al., 2016).

Four high yielding and four high ricinoleic acid accessions in the core set identified in initial evaluation trials conducted at ICAR-IIOR, Hyderabad and S.K. Nagar during 2010–12 were further evaluated separately in different years in different trials along with other germplasm accessions during 2013–16. The checks used in different trials conducted in different years were GC-3/DCS-107/Haritha. All the checks are commercial varieties. The experimental design followed was RBD with two replications. The trials in all years were conducted under rainfed conditions at Palem and ICAR-IIOR, Hyderabad and under irrigated conditions at S.K. Nagar and Mandor. The net plot size/test entry/replication was 9 sq.m at rainfed locations and 11.52 sq.m at irrigated locations. The spacing given was 90 × 60 cm at rainfed locations and 120 × 60 cm at irrigated locations. The total rainfall and other meteorological data of all four locations during crop period in 2013–14, 2014–15, 2015–16 and 2016–17 were given in the Supplementary Table 1. The data on plant height (cm), number of main stem nodes, days to 50% flowering, days to maturity, length of primary spike covered with capsules (cm), 100-seed weight (g), total seed yield (kg/ha), and oil content (%) were recorded. The 100-seed weight and total seed yield recorded in 2013–14 and 2015–16 at Palem location were not reported due to very low plant stand and low filling of seeds in experimental material because of severe gray mold disease attack during flowering and seed filling stages in 2013–14, and severe drought conditions during 2015–16. The data from all locations were analysed using INDOSTAT statistical software, Indostat services, Hyderabad, India (www.indostat.org).

2.4. Screening against leafhopper Preliminary screening of core set accessions against leafhopper was taken up along with other genotypes at Yethapur location during 2009–2011. The accessions showing high resistance reaction at Yethapur were further screened at Hyderabad, Palem and Yethapur in different years (2013–14–2016–17) in different years to confirm their reaction. Hyderabad, Palem and Yethapur are hot-spot areas for leafhopper infestation. The test entries along with susceptible checks (DPC9 and DCH-177) and resistant check (DCH-519) were planted during August month in all the years of testing at all three locations. DCH-177 and DCH-519 are commercial hybrids while DPC-9 is a commercial variety. Each entry was sown in a single row of 6 m length with spacing of 90 × 60 cm in replicated augmented block design with two replications. A single row of susceptible check, DPC-9 was grown on both the sides of test entries in sandwich method to increase leafhopper infestation. The observations on leafhopper count and hopper burn injury were recorded from 45 days after sowing at regular intervals and the peak incidence was reported (Lakshminarayana, 2005). Leafhopper count was recorded from three leaves per plant on five randomly selected plants in each entry, where each plant was considered as a replicate. The leaves were selected as one from top (excluding two top most leaves), middle (medium matured leaves) and bottom (leaving two bottom most leaves) on the main shoot. The hopper burn injury was recorded in 0–4 scale (Lakshminarayana, 2005).

3. Results 3.1. Sources of resistance to biotic stresses Fusarium wilt, Macrophomina root rot, gray mold and leafhopper are the major biotic stresses which cause near total yield loss under severe infestation conditions. Availability of reliable sources of resistance is the prerequisite to breed resistant cultivars. In order to identify reliable resistance sources in castor core set, screening of core set was done under artificial infestation conditions at different locations in different years which led to identification of several resistant sources in castor core set. 3.2. Among the 165 accessions comprising core set, eight accessions viz., RG-43, RG-111, RG-224, RG-297, RG-558, RG-2430, RG-2818, and RG2819 consistently exhibited resistance reaction with wilt incidence ranging from 0 to 18.8% in wilt sick plots at both Hyderabad and S.K. Nagar over years of testing (Table 1). These accessions also confirmed 768

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Table 1 Reaction of germplasm accessions of castor core set against Fusarium wilt in wilt-sick plots at different locations over years. Accession

RG-43

RG-111

RG-224 RG-297

RG-558 RG-2430 RG-2818

RG-2819

Year

Wilt incidence (%)

2002–03 2004–05 2006–07 2001–02 2004–05 2010–11 2001–02 2001–02 2004–05 2006–07 2011–12 2010–11 2002–03 2003–04 2004–05 2006–07 2007–08 2010–11 2002–03 2005–06 2006–07

Hyderabad Resistant accession

S.K. Nagar

Hyderabad Resistant check

S.K. Nagar

Hyderabad Susceptible check

S.K. Nagar

14.2 8.3 9.0 14.2 10.0 10.0 0.0 18.8 0.0 56.2 0.0 0.0 5.0 0.0 8.3 0.0 16.6 0.0 11.1 7.7 0.0

0.0 7.7 10.0 16.7 7.1 10.5 0.0 0.0 7.7 10 0.0 0.0 0.0 0.0 0.0 16.7 0.0 0.0 0.0 0.0 7.7

9.1 (DCS-9) 5.4 (DCS-9) 5.0 (DCS-9) 12.5 (DCS-9) 5.4 (DCS-9) 0.0 (48–1) 12.5 (DCS-9) 7.1 (DCS-9) 5.4 (DCS-9) 1.0 (DCS-9) 0.0 (48–1) 0.0 (48–1) 9.1 (DCS-9) 20.0 (DCS-9) 5.4 (DCS-9) 5.0 (DCS-9) 0.0 (DCS-9) 0.0 (48–1) 9.1 (DCS-9) 9.8 (DCS-9) 5.0 (DCS-9)

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

76.9 (Aruna) 86.4 (VP-I) 100 (VP-I) 88.2 (Aruna) 86.4 (VP-I) 91.7 (JI-35) 88.2 (Aruna) 90.9 (Aruna) 86.4 (VP-I) 90.9 (VP-I) 85.7 (JI-35) 91.7 (JI-35) 95.8 (Aruna) 88.5 (VP-I) 86.4 (VP-I) 100 (VP-I) 100 (JI-35) 91.7 (JI-35) 76.9 (Aruna) 93.8 (VP-I) 100 (VP-I)

96.6 (GAUCH-1) 100 (JI-35) 96.7 (JI-35) 97.6 (GAUCH-1) 100.0 (JI-35) 100 (JI-35) 97.6 (GAUCH-1) 98.2 (GAUCH-1) 100.0 (JI-35) 96.7 (JI-35) 97.7 (JI-35) 100.0 (JI-35) 91.9 (GAUCH-1) 98.5 (GAUCH-1) 100.0 (JI-35) 96.7 (JI-35) 100 (JI-35) 100 (JI-35) 96.6 (GAUCH-1) 100 (JI-35) 96.7 (JI-35)

(48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1)

Name of the check is given in parentheses. Table 2 Reaction of germplasm accessions of castor core set against Fusarium wilt when screened using root-dip inoculation method in greenhouse at different locations over years. Accession

RG-43 RG-111 RG-224 RG-297 RG-558 RG-2430 RG-2818 RG-2819

Year

2002 2005 2002 2005 2002 2001 2002 2012 2011 2013 2003 2004 2004

Fusarium wilt incidence (%) Hyderabad Resistant accession

S.K. Nagar

Hyderabad Resistant check

S.K. Nagar

Hyderabad Susceptible check

S.K. Nagar

0.0 0.0 18.2 9.1 15.4 4.5 0 20 0.0 15.4 0.0 0.0 0.0

0.0 5.0 0.0 8.3 7.5 0.0 0 11.8 0.0 10.0 7.1 0.0 0.0

0.0 (DCS-9) 0.0 (DCS-9) 0.0 (DCS-9) 0.0 (DCS-9) 0.0 (DCS-9) 8.3 (DCS-9) 0.0 (DCS-9) 0.0 (48–1) 16.0 (DCS-9) 0.0 (48–1) 2.0 (48–1) 0.0 (DCS-9) 0.0 (DCS-9)

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

93.3 (Aruna) 100 (JI-35) 93.3 (Aruna) 100 (JI-35) 93.3 (Aruna) 77.0 (Kranti) 93.3 (Aruna) 92.9 (JI-35) – 85.7 (JI-35) 71.4 (Kranti) 84.6 (JI-35) 84.6 (JI-35)

95.0 (GAUCH-I) 100 (JI-35) 95.0 (GAUCH-I) 100 (JI-35) 95.0 (GAUCH-I) 93.3 (GAUCH-I) 95.0 (GAUCH-I) 100 (JI-35) 100 (JI-35) 100 (JI-35) 97.5 (GAUCH-1) 100 (GAUCH-1) 100 (GAUCH-1)

(48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1) (48–1)

(GCH-4) exhibited resistance to susceptible reaction over years of screening in both sick plot and greenhouse. This may be because of decline in their genetic purity due to flaws in seed production and problems involved in maintenance of parental lines. Oil content of the six root rot resistant accessions has ranged from 48.2 to 52%. Multiple resistance to both Fusarium wilt and Macrophomina root rot were observed in four accessions namely, RG-111, RG-2430, RG2818 and RG-2819 in sick plots and greenhouse conditions. Screening against gray mold under artificial inoculation conditions in poly house resulted into identification of one resistant and one moderately resistant accession among accessions of castor core set. The accession, RG-1963 showed resistance reaction with 4.3% disease severity and RG-3088 had moderate resistance reaction (33.6% disease severity). As there was no definite source of resistance to gray mold in the entire castor genepool, the variety, 48-1, which could resist disease to some extent as compared to all the susceptible genotypes, was taken as a resistant check and whatever accession exhibiting less gray mold severity than 48-1 was considered as resistant. The disease severity was 52.3% in resistant check, 48-1 and 91.6–93.3% in susceptible checks, DCS-9 and DCH-519, which are commercial castor cultivars (Table 4).

the resistance reaction (wilt incidence: 0–15.4%) against Fusarium wilt when tested using root-dip inoculation method in pots in greenhouse at both locations in all years (Table 2). The resistant and susceptible checks have confirmed their respective reactions against wilt in both wilt sick plot and greenhouse experiment. Wilt incidence in resistant check (48-1/DCS-9) has ranged from 0 to 20% while it was 76.9–100% in susceptible check (JI-35/VP-1/GAUCH-1) in wilt sick plot. When screened using root-dip inoculation method, the wilt incidence in resistant check was 0–16% while it was 71.4–100% in susceptible check. Oil content of the eight wilt resistant accessions has ranged from 46 to 52%. RG-2819 had the highest oil content (52%) followed by RG-2818 (51%). Six accessions viz., RG-111, RG-2035, RG-2430, RG-2818, RG-2819 and RG-2821 in castor-core exhibited resistance reaction against Macrophomina root rot (root rot incidence: 0–18.7%) in root rot sick plot at Junagadh (Table 3) in all the years of screening. The same accessions confirmed resistance reaction (root rot incidence: 0–19.2%) in greenhouse when screened using stem-tape inoculation method. The resistant and susceptible checks have not exhibited their true reaction against root rot. Both resistant check (JI-357) and susceptible check 769

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(Table 6) while the high yielding hybrid, DCH-519 and variety, GC-3 had 87.5-88.7% ricinoleic acid content. The high ricinoleic acid type accession, RG-2685 yielded at par with the high yielding check variety, GC-3 (Table 7). It possessed 48.7% mean oil content at par with GC-3 (48.4%). RG-2685 was comparable to GC-3 in most of the agronomic and phenological traits (Supplementary Table 2). One core set accession, RG-1647 possessed higher mean 100-seed weight (51.3 g) than the check varieties, GC-3 (35.3 g) and DCS-107 (30.8 g) when tested across locations. It gave 2607 kg/ha mean seed yield under irrigated conditions, which was comparable to seed yield of check, GC-3 (2647 kg/ha), however its yield under rainfed conditions (1751 kg/ha) was far less than that of GC-3 (2346 kg/ha) (Table 8). RG-1647 recorded 50.4% mean oil content while the check, GC-3 had 50% and DCS-107 had 49.2% oil content. The wilt and leafhopper resistant accession, RG-43 had low number of nodes (10) on main stem as compared to the variety check, GC-3/DCS-107/Haritha (16), and days to 50% flowering in RG43 has ranged from 48 to 57 days while the normal duration checks reached to 50% flowering in 52–68 days across locations (Table 9). However, its yield performance and other agronomic and economic traits were not comparable to GC-3 (Supplementary Table 3). RG-43 had 46% mean oil content.

Table 3 Reaction of germplasm accessions of castor core set against Macrophomina root rot under artificial infestation conditions in root rot sick plot and greenhouse. Accession

Year

Root rot sick plot RG-111 a 2015–16 RG-2035 2009–10 2010–11 RG-2430 a 2010–11 RG-2818 a 2004–05 2005–06 2006–07 2007–08 2010–11 a RG-2819 2003–04 2004–05 2005–06 2006–07 2007–08 RG-2821 2010–11 b Greenhouse RG-111 2016–17 RG-2035 2011–12 2015–16 RG-2430 2011–12 RG-2818 2011–12 RG-2819 2014–15 RG-2821 2011–12 2016–17 a b

Root rot incidence in sick plot (%) Resistant accession

Resistant check

Susceptible check

2.9 0.0 0.0 0.0 0.0 0.0 13.0 18.1 0.0 0.0 5.0 0.0 6.2 0.0 0.0

22.2 27.4 69.8 69.8 – – 12.5 30.2 69.8 – – – 12.5 30.2 69.8

(JI-357) (JI-357) (JI-357) (JI-357)

(JI-357) (JI-357) (JI-357)

80.1 91.8 84.3 84.3 85.5 87.2 84.5 84.6 84.3 87.2 85.5 87.2 84.5 84.6 84.3

19.2 4.8 15.6 0.0 5.3 11.1 0.0 12.5

10.7 11.1 11.1 11.1 11.1 30.0 11.1 10.7

(JI-357) (JI-357) (JI-357) (JI-357) (JI-357) (JI-357) (JI-357) (JI-357)

85.9(GCH-4) 12.5 (GCH-4) 22.2 (GCH-4) 12.5 (GCH-4) 12.5 (GCH-4) 90.0 (GCH-4) 12.5 (GCH-4) 85.9 (GCH-4)

(JI-357) (JI-357) (JI-357)

(GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4) (GCH-4)

4. Discussion The 165 castor germplasm accessions incorporated in core set were found to be diverse when agro-morphologial data were used for constructing the core set (Sarada and Anjani, 2013). Molecular analysis of the core set has revealed absence of population structure indicating diverse nature of the accessions at molecular level (Senthilvel et al., 2016). This core set serves as a diverse base material to breeders who want to initiate castor breeding programme, however, in the centres where large castor breeding programmes are being taken up, utilization of the entire core set in breeding programme is not feasible. Under such situations, if trait-specific accessions are identified within the core set, it would be of great use to breeders to incorporate them immediately in the breeding programmes as donors of the specific trait. The present study spread over years at different locations has identified several sources of resistance to major diseases of castor such as Fusarium wilt, Macrophomina root rot, gray mold and leafhopper besides identification of high ricinoleic type and high yielding accessions and accessions with specific agronomic and quality traits. Fusarium wilt (F. oxysporum f.sp. ricini) is a devastating soil borne disease in castor especially when the crop is repeatedly grown in the same field year after year. It is also associated with seed when seeds are collected from infected plants. Wilt affects the crop at all growth stages and causes 39–85% yield loss depending up on the stage of the crop at the time of infection (Pushpavathi et al., 1998; Dange, 2003). Fusarium wilt was reported in many castor growing countries such as Russia, India, Morocco, China, Mexico etc. (Moshkin, 1986; Podukuichenko, 1991). It was first reported in Morocco (Rieuf, 1953), and in India in 1974 (Nanda and Prasad, 1974). It is difficult to manage wilt disease

also resistant to Fusarium wilt. stem tape inoculation method.

Oil content of resistant accession, RG-1963 was 48.6% while that of RG3088 was 48.1%. 3.3. Sources of resistance to leafhopper Among 165 core set accessions, five accessions viz., RG-43, RG-631, RG-1621, RG-3037 and RG-3067 exhibited resistance reaction against leafhopper (0–1 hopper burn on 0–4 scale) at all the three locations in all years of screening (Table 5). RG-43 was also found to be resistant to Fusarium wilt. The resistant check, DCH-519, the commercial castor hybrid, showed 0–1 hopper burn scale while the DPC-9 and DCH-177 exhibited 2–4 hopper burn scale at different locations. Oil content of RG-43, RG-631, RG-1621, RG-3037 was 46, 51, 51, 51, 52%, respectively. 3.4. Sources of promising qualitative and quantitative traits Among the 165 core set accessions evaluated at multilocations for ricinoleic acid level, and economic and phenological traits, four accessions viz., RG-408, RG-2451, RG-2685, and RG-3233 stably expressed high levels of ricinoleic acid (90.4–91%) across locations

Table 4 Reaction of germplasm accessions of castor core set against gray mold under artificial inoculatiom conditions in poly house. Accession

Mean gray mold severity (%) Days after inoculum spray

RG-1963 RG-3088 48-1 (RC) DCS-9 (SC) DCH-519 (SC)

3

4

5

6

7

8

0.0 ± 0.0 0.60 ± 0.6 4.0 ± 1.0 10.0 ± 0.0 11.6 ± 1.6

0.0 ± 0.0 2.3 ± 1.4 10.0 ± 2.8 28.3 ± 1.6 26.6 ± 1.6

0.0 ± 0.0 8.3 ± 4.4 20.0 ± 2.8 46.6 ± 4.4 43.3 ± 1.6

0.0 ± 0.0 15.0 ± 7.6 30.6 ± 0.6 65.0 ± 2.8 62.3 ± 1.4

1.6 ± 1.6 22.6 ± 9.9 41.3 ± 0.6 78.3 ± 4.4 81.6 ± 1.6

4.3 ± 3.5 33.6 ± 12.8 52.3 ± 2.3 91.6 ± 6.0 93.3 ± 2.4

RC: resistant check; SC: susceptible check; value follwed mean ± is SEm.

770

Industrial Crops & Products 112 (2018) 766–774 2 4 3 2 4 4 3b 2 4 3 4c 4 3c 4c 4 4 4 4c 4 3c 4 4 4 4 4 4 4 4 4 4 9.3 ± 0.7 22.3 ± 0.1 38.7 ± 2.4 9.3 ± 0.7 22.3 ± 0.1 22.3 ± 0.1 28.6b ± 0.9 9.3 ± 0.7 22.3 ± 0.1 38.7 ± 2.4 0 0 0 0 0 0 1 0 0 0 1 0 1 1 0 0 1 1 0 1

c

b

a

RG-1621 RG-3037 RG-3067

RG-631

Resistant check, DCH-519. susceptible check, DPC-9. susceptible check, DCH-177; LH: No. of leafhopper/3 leaves/plant; HB: hopper burn (0–4 scale); H: Hyderabad; P: Palem; Y: Yethapur.

0.3 0.2 0.1 0.3 0.2 0.2 0.6 0.3 0.2 0.1 4.6 ± 0.2 2.7 ± 0.3 9.0 ± 1.0 4.6 ± 0.2 2.7 ± 0.3 2.7 ± 0.3 15.0 ± 0.5 4.6 ± 0.2 2.7 ± 0.3 9.0 ± 1.0 4.0 2.4 0.1 4.0 2.4 2.4 1.8 4.0 2.4 0.1 ± ± ± ± ± ± ± ± ± ± 15.0 11.3 22.9 15.0 11.3 11.3 33.8 15.0 11.3 22.9 25.5 12.5 16.0 25.5 12.5 12.5 17.1 25.5 12.5 16.0 0 0 0 0 1 1 0 0 – 0 1 0 0 1 0 1 1 0 0 – 0.4 0.7 0.5 0.3 0.3 0.2 1.5 0.3 0.4 0.3 1.6 1.3 2.2 4.1 7.3 7.6 0.0 2.5 9.6 1.3 15.8 ± 0.2 8.4 ± 1.2 20.6 ± 0.5 16.0 ± 2.6 9.2 ± 0.9 14.3 ± 0.9 56.5 ± 7.2 5.8 ± 2.8 10.2 ± 3.0 – 27.2 ± 1.6 6.8 ± 0.0 13.1 ± 1.9 12.4 ± 0.2 17.9 ± 3.3 22.9 ± 3.3 30.7 ± 0.3 15.6 ± 5.8 20.2 ± 4.6 8.8 ± 2.2 2013–14 2014–15 2015–16 2013–14 2014–15 2014–15 2016–17 2013–14 2014–15 2015–16 RG-43

P

Y

± ± ± ± ± ± ± ± ± ±

0.3 0.3 0.9 0.8 0.3 0.7 0.0 0.02 0.5 1.3

P

Y

H

± ± ± ± ± ± ± ± ± ±

8.9 0.1 1.0 8.9 0.1 0.1 1.9 8.9 0.1 1.0 H H

P

LH (Mean ± SE) HB LH (Mean ± SE)

a

Resistant check Resistant accession Year Accession

Table 5 Screening of castor core set against leafhopper using infester-row method at different locations over years.

through chemical control. Eventually growing a resistant cultivar is an effective means to manage it. Availability of stable sources of resistance is essential to breed resistant cultivars. Earlier Anjani et al. (2014) have reported 13 Fusarium wilt resistant castor germplasm accessions, of which three accessions viz., RG-43, RG-111 and RG-297 were included in castor core set. In addition to these accessions, five more accessions viz., RG-224, RG-558, RG-2430, RG-2818, and RG-2819 of castor core set were found to be resistant to Fusarium wilt in the present study. These eight accessions would serve as reliable stable sources of resistance to castor breeders. Since these accessions are not related to each other, they act as diverse sources of wilt resistance for immediate utilization in breeding programme to breed wilt resistant cultivars with broad genetic base. Macrophomina root rot (M. phaseolina) is a devastating soil borne disease in dry lands. It causes seedling blight and dieback due to aerial infection (Maiti and Raoof, 1984), spike, stem and twig blights, root rot and collar rot (Moses and Reddy, 1987). This disease has been reported from Brazil, Costa Rica, east Africa, India, Palestine, Philippines, South Africa, Sri Lanka, United States and West Indies (Grezes-Besset et al., 1996; Claudino and Soares, 2014; Nagaraja and Krishnappa, 2016). High temperatures and water stress enhance the disease (Das and Srivastava, 1992); seeds collected from infected plants also spread root rot disease (Nagaraja and Krishnappa, 2016). Around 20–60% yield loss due to Macrophomina root rot was reported in castor (Das and Prasad, 1989). Hence, growing resistant cultivar is an ideal approach to manage this disease. However, none of the released cultivar is resistant to root rot. Among 169 core set accessions, six accessions namely, RG-111, RG2035, RG-2430, RG-2818, RG-2819 and RG-2821 consistently exhibited resistance reaction against root rot. These are valuable accessions to utilize as sources of resistance in root rot resistance breeding. Gray mold (B. ricini) is the most destructive disease of castor. It mainly infects inflorescences and capsules, and under severe disease condition it spreads to leaves, petioles and stem (Soares, 2012). This disease has world-wide distribution and was reported in almost all castor growing countries (Godfrey 1923; Kolte, 1995; Soares, 2012). Temperatures around 25 °C and high relative humidity are highly favourable for the disease development (Godfrey, 1923). Disease incidence and severity were highly correlated with temperature and duration of leaf wetness (Sussel et al., 2011). Gray mold can cause yield losses up to 100% (Godfrey, 1923; Prasad and Kumaraswamy, 2017) as it mainly infects inflorescences and capsules. Infection can lead to complete destruction of the spike if weather conditions were favourable. Chemical control is ineffective, hence, growing resistant cultivars is the only strategy to manage gray mold. However, no resistant cultivars have been developed so far in castor due to non-availability of sources of resistance. The present study has identified two accessions, RG-1963 and RG-3088 exhibiting resistance and moderate resistance reactions against gray mold. As no other reliable sources of resistance against gray mold are identified so far in castor, RG-1963 can be utilized as a resistance source in gray mold resistance breeding programme as it exhibited resistance reaction under controlled artificial inoculation conditions in poly house. Leafhopper (E. flavescens) is widely distributed across many countries including almost all countries in Europe, India, China, Cambodia, Indonesia, Iraq, Israel, Japan, Malaysia, Pakistan, Philippines etc. (CABI, 1974). Leafhopper damage could cause yield loss to the extent of 22–89% in castor (Jayaraj, 1966; Lakshminarayan and Duraimurugan, 2014). Insecticide application is effective in controlling this pest but the length of effective protection can vary and additional foliar insecticide sprays are needed to control leafhopper, which consequently increases cost of production. Host-plant resistance is the most reliable, economical and eco-friendly measure to control leafhopper. The five leafhopper resistance sources viz., RG-43, RG-631, RG-1621, RG-3037 and RG3067 identified in this study have consistently exhibited resistant reaction when tested at different locations and years. These accessions would serve as stable sources of leafhopper resistance in breeding

173.8 ± 11.0 104.8 ± 9.6 73.1 ± 0.3 173.8 ± 11.0 104.8 ± 9.6 104.8 ± 9.6 88.3 ± 0.3 173.8 ± 11.0 104.8 ± 9.6 73.1 ± 0.3

37.4c ± 11.8 40.2 ± 2.3 61.1c ± 0.9 37.4c ± 11.8 40.2 ± 2.3 40.2 ± 2.3 55.8 ± 3.8 37.4c ± 11.8 40.2 ± 2.3 61.1c ± 0.9

H Yc P H H Y

HB

P

Y

LH (Mean ± SE)

Susceptible check

b

HB

P

Yc

K. Anjani et al.

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Table 6 Ricinoleic acid content in high ricinoleic type germplasm accessions in castor core set at different locations. Accession

Year

Ricinoleic acid content ± %

Oil content (%)

Irrigated

Rainfed

Mandor RG-408 RG-2451 RG-2685 RG-3233 GCH-7 (check) GC-3 (check)

2014–15 2014–15 2014–15 2015–16 2016–17 2014–15 2015–16 2015–16

91.6 90.0 90.5 91.6 91.0 89.2 88.6 87.4

± ± ± ± ± ± ± ±

0.28 0.27 0.28 0.45 0.33 0.25 0.42 0.35

Mean

S.K. Nagar

Palem

Hyderabad

90.5 91.3 91.5 91.2 90.0 88.5 87.5 86.8

90.5 – 91.4 – 91.0 – 88.7 88.6

90.2 90.0 90.6 90.0 92.0 88.6 87.1 87.4

± ± ± ± ± ± ± ±

0.26 0.22 0.24 0.28 0.34 0.21 0.24 0.23

± 0.32 ± 0.35 ± 0.31 ± 0.27 ± 0.35

± ± ± ± ± ± ± ±

0.33 0.30 0.29 0.24 0.31 0.33 0.30 0.29

90.7 90.4 91.0 90.9 91.0 88.7 87.9 87.5

Irrigated

Rainfed

Mean

Mandor

S.K. Nagar

Palem

Hyderabad

46 47 44 50 45 46 47 50

46 45 44 50 48 47 46 49

49 – 46 – 48 – 47 50

47 45 45 48 45 48 45 47

47 46 45 49 47 47 46 49

The value after mean ± is standard error. Table 7 Seed yield and oil content of high ricinoleic type accession, RG-2685 at different locations in 2015–16. Accession

Seed yield (kg/ha)

Oil content (%)

Irrigated

RG-2685 GC-3 (check) SEm ± CV (%) CD (P = 0.05)

Rainfed

Mean

Mandor

S.K. Nagar

Hyderabad

1424 1532 34.2 14 320

3483 3576 39.4 7 82

464 273 10.1 13 97

Irrigated

1790 1794 – – –

Rainfed

Mandor

S.K. Nagar

Hyderabad

49.7 49.6 0.2 1.8 1.8

46.3 51.5 0.22 2 –

50.2 44.5 3.19 1.4 1.1

Mean

48.7 48.4 – – –

Table 8 Seed yield, oil content and 100-seed weight of RG-1647 at different locations in 2013–14. Accession

Irrigated

Rainfed

Mandor

RG-1647 GC-3 (check) DCS-107 (check) SEm ± CV (%) CD (P = 0.05)

S.K. Nagar

Mean

Hyderabad

SW (g)

YLD (kg/ha)

OC (%)

SW (g)

YLD (kg/ha)

OC (%)

SW (g)

YLD (kg/ha)

SW (g)

YLD (kg/ha)

OC (%)

49.4 36.5 – 0.86 9.2 13.7

2591 2287 – 73 13 162

50.4 49.6 – 0.06 0.38 0.13

52.7 34.1 – 0.66 6.8 4.9

2622 3007 – 137 18 302

50.1 50.8

51.0 35.3 –

2607 2647 –

52.9 – 30.8 0.48 5.2 5.2

1751 – 2346 81 16 178

50.7 – 49.2 0.07 0.52 0.52

0.05 0.35 0.87

SW: 100-seed weight; YLD: total seed yield; OC: oil content. Table 9 Number of nodes, days to 50% flowering and oil content of RG-43 at different locations in 2014-15. Accession

Irrigated

RG-43 Check a SEm ± CV (%) CD (P = 0.05)

Days to 50% flowering

Number of nodes Rainfed

Mean

M

S

P

H

13 17 0.33 9 3.4

12 17 0.31 9 2.4

8 10 0.33 13 3.0

8 18 0.25 8 2.0

10 – – – –

Irrigated

Oil content (%)

Rainfed

Mean

M

S

P

H

56 68 1.13 8 12

57 66 1.19 1 2

52 52 1.03 8 11

48 66 0.7 6 2

53 – – – –

Irrigated

Rainfed

Mean

M

S

P

H

45 47 0.13 1.4 0.2

46 46 0.11 1.4 0.5

47 45 0.11 1.2 0.2

46 48 0.11 1.3 0.2

46.0 46.7 – – –

M: Mandor; S: S.K. Nagar; P: Palem; H: Hyderabad. a Check was GC-3 at Mandor and S.K. Nagar, Haritha at Palem, and DCS-107 at Hyderabad.

reported in castor germplasm (Rojas-Barros et al., 2004; Praduman and Anjani, 2016). The gene, FAH12, which is directly responsible for synthesis of ricinoleic acid (van de Loo et al., 1995), has been identified in endosperm of castor seed, however, ricinoleic acid content in the transformed Arabidopsis expressing FAH12 was not more than 17%.

programmes aiming to develop leafhopper resistant cultivars. Castor oil is the only oil which contains approximately 85–88% ricinoleic acid. This makes castor oil a unique source for preparation of thousands of derivatives suitable to prepare a number of products in several industrial fields. Diversity in ricinoleic acid content was 772

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Investigations on drought tolerance using castor core set accessions were reported earlier. Radhamani et al. (2014) identified nine core set accessions viz., RG-2022, RG-2184, RG-2195, RG-2474, RG-2582, RG3013, RG-3063, RG-3116 and RG-3233 as sources of drought tolerance exhibiting low drought susceptibility index (0.09–0.47) under imposed drought conditions in the field. The drought tolerant accession, RG3233 was also identified as a high ricinoleic type (91%) accession in the present study. Lakshmamma et al. (2004) identified RG-72 included in core set for drought tolerance. Radhamani et al. (2012) identified the core set accession namely, RG-2474 for good germination percentage, and shoot and root length under PEG induced drought tolerance conditions in the laboratory. Two core set accessions, RG-3063 and RG-941 have been earlier identified for possessing long root length, high root dry weight, high leaf area index, high total dry matter, low carbon isotope discrimination (13C) and high 18O values, which are surrogate traits for measuring water use efficiency in plant species (Lakshmamma et al., 2010a; Lakshmamma et al., 2010b). Five accessions of core set viz., RG-43, RG-72, RG-297, RG-2818, and RG-2819 were registered with Plant Germplasm Registration Committee, Indian Council of Agricultural Research-National Bureau of Plant Genetic Resources (ICAR-NBPGR), New Delhi, India (Anjani, 2012; Anjani et al., 2014). When the present findings and other reports on castor core set accessions were consolidated, there were total 39 core set accessions identified for specific traits that are useful to castor researchers. Except RG-2451 and RG-111, all other trait-specific accessions were of Indian origin, which were collected through conduction of explorations in 12 States in India viz., Assam, Andhra Pradesh, Bihar, Gujarat, Himachal Pradesh, Karnataka, Maharashtra, Madhya Pradesh, Odisha, Rajasthan, Tamil Nadu and Uttar Pradesh (Anjani, 2012). RG2451 was an introduction (PI-258363) from USA and RG-111 was from former USSR. The trait-specific accessions reported in the present study would serve as instant basic sources for the specific traits, and play an important role in diversifying the genetic base of working collection of castor breeders for developing improved castor cultivars with broad genetic base.

McKeon and Lin (2002) have suggested that the castor FAH12 gene is not sufficient by itself to produce high levels of ricinoleate in other plants. Hyun Uk et al. (2011) have identified a PDAT1-2 gene which was able to significantly increase ricinoleic acid content from 17 to 25% in transgenic Arabidopsis. So far no high ricinoleic acid type (90%) commercial castor cultivars were developed either through transgenic or conventional breeding method. Any increase in ricinoleic acid content in castor oil beyond the existing level (85–88%) in castor cultivars would increase the value of oil, and would be highly beneficial to industry. In castor core set four accessions viz., RG-408, RG-2451, RG2685 and RG-3233 possessed stably high ricinoleic acid content (90.4–91%) across locations. No environmental affect on ricinoleic acid content of these accessions was observed when tested at different locations under both rainfed and irrigated conditions. These accessions would serve as reliable sources of high ricinoleic acid content in order to breed high ricinoleic type castor cultivars. The high yielding-high ricinoleic acid type accession, RG-2685 can be utilized as a donor for both high yield and high ricinoelic acid content. Among the yield contributing traits, 100-seed weight is one of the reliable traits (Aswani et al., 2003) as it is controlled by additive gene action (Solanki and Joshi, 2000) and positively correlated with seed yield in castor (Aswani et al., 2003; Patel and Nakarani, 2016). The 100-seed weight among the released castor cultivars is 28–32 g. The accession, RG-647 with significantly higher 100-seed weight (51.2 g) across locations would serve as a source of high seed weight in castor breeding programmes. Castor is essentially a perennial shrub though cultivated as an annual oilseed crop. In dry land areas, castor crop generally undergoes moisture stress at around 60–65 days after planting which coincides with flowering and capsule formation stages of the primary spike, which is the major contributor to total seed yield (Moshkin, 1986). Castor inflorescence is a monoclinous monoecious spike, and the ratio of female to male flowers on a spike is largely influenced by environment especially by moisture stress and high temperatures at the time of flowering. Moisture stress induces production of more male flowers on spike thus reduces seed yield. All the released castor cultivars take 60–65 days to reach 50% flowering. In castor, number of nodes on main stem gives a clue to maturity duration of the genotype as it is highly positively correlated to days to 50% flowering and days to maturity, hence, lower the node number earlier the genotype (Bhatt and Reddy, 1981; Anjani, 2010). Node number is a reliable trait for breeding early maturing lines as it is controlled by additive gene action (Golakia et al., 2007). The days taken to reach 50% flowering in the early duration accession, RG-43 and in the medium duration check variety were in accordance with number of nodes on main stem (Table 9). The accession, RG-43 had reached to 50% flowering in 48–57 days while the checks took 52-68 days. Across the locations under rainfed and irrigated conditions, RG-43 consistently exhibited early flowering nature. A stable source of early maturity is needed to breed early maturing castor cultivars. In addition to earliness, RG-43 is resistant to wilt and leafhopper. Hence, it can be utilized at once as a multiple donor for earliness and resistance to Fusarium wilt and root rot. The diversity in the vast collection of castor germplasm continues to contribute to genetic improvement of castor for productivity. However, large size of the collection and non-availability of multilocation data on many accessions has resulted in low use of germplasm leading to narrow genetic base. These problems would be overcome, if the core set was efficiently used in castor improvement programme. To reduce the difficulties involved in utilization of 165 diverse accessions of core set, the present study has identified several trait-specific accessions in core set which are useful for castor genetic improvement. The information generated in this study would be of great value to castor breeders in their efforts to utilize trait-specific diverse sources. Identification of core set accessions with a combination of two or more traits also would permit use of one donor for multiple traits. This study has identified total 26 trait-specific accessions in core set.

Acknowledgements The authors are highly thankful to the Director, ICAR-Indian Institute of Oilseeds Research (ICAR-IIOR), Hyderabad, India for providing all the facilities and guidance while carrying out the research at ICAR-IIOR and allowing us to test castor core germplasm accessions at different centres under All India Coordinated Research Project (AICRP) on Castor. We are also thankful to castor researchers at Junagadh, S.K. Nagar, Palem and Yethapur for testing the core set accessions under various trials of AICRP on Castor. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.indcrop.2018.01.002. References Anjani, K., Raoof, M.A., Vardhana, Ashoka, Reddy, P., Hanumanta Rao, C., 2004. Sources of resistance to major castor (Ricinus communis L.) diseases. Plant Genet. Resour. Newsltr. 137, 46–48. Anjani, K., Raoof, M.M., Desai, A.G., 2014. Evaluation of world castor (Ricinus communis L.) germplasm for resistance to Fusarium wilt (Fusarium oxysporum f. sp. ricini). Euro. J. Plant Pathol. 139, 567–578. Anjani, K., 2010. Extra-early maturing germplasm for utilization in castor improvement. Ind. Crop Prod. 31, 139–144. Anjani, K., 2012. Castor genetic resources: a primary gene pool for exploitation. Ind. Crop Prod. 35, 1–14. Aswani, K., Sangwan, R.S., Jatasra, D.S., 2003. Correlation and path co-efficient analysis in castor (Ricinus communis L.) under dry land conditions. Indian J. Dryland Agric. Res. Dev. 18, 89–91. Bhatt, D., Reddy, T.P., 1981. Correlation and path analysis in castor (Ricinus communis L.). Can. J. Genet. Cytogenet. 23, 523–531.

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