Williams, R.J.

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THE INTERNATIONAL TESTING PROGRAM: AIMS, PROGRESS AND PROBLEMS SEEN FROM IlTA R. J. Williams International Institute of Tropical Agriculture, Ibadan During the period 1971 to 1975 a large portion of the cowpea world germplasm collection was screened at IITA for susceptibility to the major diseases occurring in the region, and more than 100 multiple resistant lines were identified. In 1974 the GLIP pathology program, in cooperation with several research workers in other tropical countries, initiated an Interna-tional Cowpea Disease Nursery Program (ICPNP) in an attempt to identify broad spectrum stable resistance to many different populations of pathogens (including some that do not occur at IITA) over a broad range of environmental conditions. In addition to providing information on varietal resistance, the ICDNP also serves as a means of distributing useful cowpea germplasm to research workers in a position to make immediate use of desirable traits and as a means of promoting exchange of materials and ideas between research workers. Two international disease nurseries were intiated in 1974. The International Cowpea Disease Nursery (ICDN), consisting of 100 lines which show multiple resistance at Ibadan, was sent to cooperators in Brazil, Colombia, Puerto Rico, Tanzania, India and the Philippines. The second nursery, the International Cowpea Mosaic Virus Nursery (ICPMVN),consisting of 12 lines that are resistant to the spherical beetle-transmitted cowpea mosaic virus at Ibadan, was sent to cooperators in Brazil, Colombia, El Salvador, Puerto Rico, Trinidad and India, for testing against local CPMV strains. ICDN Resul ts At the time of writing results of the ICDN have been received from Puerto Rico, India and Nigeria. A summary of the results from each loca-tion follows: A. Puerto Rico (Cooperator Dr. N.G. Vakili) The ICDN was planted at Mayaguez (5 June 1974) and Isabela (19 June 1974) together with lines 10-R6l and 10-R65, which are resistant and susceptible respectively to cowpea mosaic virus (CPMV), powdery mildew and cercospora leaf spot. All entries were directly inoculated with a local CPMV isolate and a local bacterial blight isolate. Rhizoctonia stem rot and web blight, powdery mildew, cercospora leaf spot and target spot also occurred widely in both plantings. The data indicate that: (a) 13 ICDN lines were resistant, and 2 ICDN lines were moderately resistant, to the Puerto Rican CPMV strain. However several of the lines resistant to CPMV in Puerto Rico are highly susceptible - 67 -in Nigeria, and vice vers~ indicating the presence of different pathogenic CPMV strains; (b) seven of the ICDN lines (including TVu 1190) remained free from bacterial blight after two heavy inoculations; (c) most lines were susceptible to Rhizoctonia web blight but entry 96 (TVu 4539) appeared to be resistant; (d) ninety of the 100 test lines were resistant to cercospora leaf spot (CLS). (e) forty-Six ICDN lines were susceptible to powdery mildew. This is valuable information because there is no opportunity to screen for susceptibility to this disease at IITA. (f) only three entries developed target spot (Corynespora cassiicola) and these three lines are also susceptible to this disease in Nigeria. B. India (Cooperator Dr. P. N. Patel). The ICDN was grown at the IARI, New Delhi during the Kharif season, 1974. Poor rainfall distribution hampered disease development but information was obtained on susceptibility to aphid attack and cercospora leaf spot. The lines are presently being tested for reaction to bacterial blight and to three cowpea viruses; of major interest are the facts that: (a) none of the ICDN lines were susceptible to cercospora leaf spot, though the local susceptible line developed symptoms. (b) six lines were highly resistant to the aphid Aphis craccivora Kock and 16 lines were moderately resistant to the insect. The resistance has since been checked by careful laboratory experi-mentation and the high degree of resistance has been convincingly confirmed (P.N. Patel, personal communication). (c) TVu 410, TVu 1563, TVu 2331 and TVu 2276 appeared to be resistant to the spherical aphid-borne cowpea mosaic virus. C. Nigeria (Cooperator Dr. R.J. Williams) The ICDN lines were planted on the IITA farm in late April 1974 and were exposed to the pathogens causing anthracnose, bacterial pustule, cercospora leaf spot and rust by inoculating highly susceptible spreader lines planted two weeks before the test lines at both ends of each test row. Disease development was good during the heavy June rains, and in addition to the above diseases target spot bacterial blight and Cercospora canescens leaf spot also were widespread in the planting. In an adjacent field all the ICDN lines were mechanically inoculated with two CPMV isolates. The complete results are given in the full report but of major interest are the points: - 68 -(a) 61 ICDN lines were innnune or highly resistant to the: four major bacterial and fungal diseases - anthracnose, bacterial pustule, cercospora leaf spot and rust. (b) 11 of the 61 lines with multiple resistance to the bacterial and fungal diseases were also resistant to the two CPMV isolates (TVu's 201, 347, 408-PZ, 410, 537, 697, 746, 1190, 1283, 2430-Pl and 34l5). (c) nine lines showed differential reactions to the two CPMV isolates indicating pathogenic variability amongst CPMV strains; (d) 19 lines were free from target spot and as the disease was so widespread in the planting they have been designated resistant. D. OVerall Resistance Rating of ICDN Lines In order to compare overall performance numerical values have been given to the various disease reaction categories for each disease at all locations according to the follOWing system: Reaction Category HR and R (Resistant) o (freedom from disease but line not directly exposed to Inoculum) LS (low susceptible) D, R/S (Differential reaction to isolates or segregating) MS, MR (moderately susceptible) S (susceptible) HS (highly susceptible) Numerical Score 6 5 4 3 2 1 o The overall resistance rating, derived by adding up the score for each disease at each location, is summarized in Table 1. The line TVu 1190 (recently registered as VITA 3) is outstanding with a resistance rating (RR) of 74 and is followed by TVu 410 (RR 70), TVu 2331, which was included as a rust susceptible indicator (RR 62), and TVu's 408-P2 and 1563 (RR 61). The trial mean resistance rating was 50.67. Fifty-four lines had better ratings than the trial mean, and 86 lines had better ratings than 50% of maximum possible score. ICPMVN Results At the time of preparation of this report ICPMVN results have been received from cooperators in Brazil, El Salvador, India, Nigeria, Puerto Rico and Trinjdad. The results are combined and summarized in Table 2. Table 1. Resistance rating 74 70 62 61 60 59 58 57 56 55 54 53 52 51 50** 49 48 47 46 44*** 43 42 40 39 38 37 36 35 31 - 69 _ Resistance ratings of 104 cowpea lines in the 1974 ICDN program. 1190 410 2331* 408-P2, 1563 746, 3415 Line(s) (TVu No's) 43, 347, 4535, 4538 2276 57* 857, 4539, 4640 196, 1404, 1593, 1962, 2430-P1, 3511 201, 317, 461, 563-P1, 1961, 3273 131, 455. 1233, 1461-P2, 1480-P1 853, 1037, 1452. 1460-P2, 2512 346, 401, 433, 647, 1560, 2455-P2, 2460, 4543 191, 984, 985, 1000, 1027, 1938, 2000, 4537 154, 356, 515, 527, 697, 726, 1592, 2433. 2470, 3522-P1, 4536, 6665 62-P1, 264-P2, 1446, 1595, 2475-P2 381. 1614, 3349 476-P2, 735-2, 1065, 1113, 2366. 2480 459, 1566, 1963, 2616-P2, 4544, 6666 1565, 2545, 2549, 4545, 6663 155-P1, 179-P1 528, 1637-P3, 2363-P1 91*, 280 1485-P1 1423-P1 662-P1 4541 612 76* * Cowpea lines known to be susceptible to certain diseases included as indicators. ** Trial mean resistance rating 50.67 *** 45 is 50% of maximum possible rating I 0 ..... Table 2. Reactions of 12 cowpea lines to nine CPMV isolates in six countries in the 1974 ICPMVN. Line Brazil El Salvador IndiaY Nigeria Puerto Rico (2 isolates) (1 isolate) (1 isolate) (2 isolates) (1 isolate) 113 (S )'!:.l NII~/ HR HR S 274 (S) N + CLL HR HR HS 310 (S) N + CLL HR HR HS 410-Pl (S) CLL HR HR 433 470 486 746 1190 2769 3563 3650 (S) CLL HR HR (5) CLL HR HR (S) NLL HR UR (S) N + CLL HR HR HR N + CLL HR HR (S) CLL HR HR (S) CLL IlR HR (S) N + CLL IlR HR 1/ Virus identity unsure but believed to be CPMV y IlR = No systemic symptoms MR/MS = Moderately resistant/susceptible S = Susceptible HS = Highly susceptible (S) = Degree of susceptibility not indicated 2/ Systemic reaction not given. NLL = necrotic local lesions eLL = chlorotic local. lesion US US US MS/MR S S S Trinidad (1 isolate) R (S) (S) (S) (S) (S) (S) (S) (S) (S) (S) (S) - 71 _ All 12 lines were symptoms free in the Nigerian and Indian tests. It is not clear whether the reactions in El Salvador were local lesions only with no ~ystemic symptoms, and clarification has been requested from the c~operator ~n El ~alvador. In Brazil and Puerto Rico the only line showing some degree of res~stance was TVu 1190 (VITA 3) which was highly resistant to two CPMV isolates in Brazil and moderately resistant to one CPMV isolate in Puerto Rico •. The susc~ptibility of ten of the lines at three locations whereas they were.h~ghly res~stant.at.two locations indicates the presence of pathogenic stra~ns of CPMV, but ~t ~s encouraging that TVu 1190 is resistant to most of them. Discussion The 1974 International Cowpea Disease Nursery Program, whilst being conducted at only a few locations, highlights the importance of a coordinated multilocational disease resistance testing program and provides information that indicates the possibilities for the achievement of the objectives stated at the heginning of this report. As a result of the 1974 program we know that: resistance to cercospora leaf spot or CPMV in Nigeria does not necessarily mean resistance to these diseases in Latin American countries; that we can screen for resistance to powdery mildew in Puerto Rico and to aphids in India; that lines like TVu's 1190, 410, 2331, 408-P and 1563 have a much broader spectrum of resistance than many other lines which are multiple-resistant lines at IITA and that already seed of these broadly resistant lines has already been distributed to researchers in several tropical countries. The 1974 program marks a small and useful beginning to the ICDNP but many additional locations are required to increase the range of variability of pathogens and pathogen populations. Locations are required where ephiphytotics of Septoria leaf spot, Ascocthyta leaf spot, Synchytrium false rust, Fusarium wilt occur annually, and where the pathogens causing rust, mildew, anthracnose, mosaic and others may have evolved under different selection pressures to produce different pathogenes. It is hoped that" possibilities tor identification of broad based multiple disease resistance indicated by the results presented in this report will stimulate many other research workers to participate in the International Cowpea Disease"Nursery Program. Cooperators in the 1974 ICDNP The ICDNP is an informal international cooperative effort. Scien-tists who participated in the 1974 ICD~IP are: Dr. Luis H. Camacho ICA Apartado Aereo 233 Palmira Colombia Dr. N. G. Mamicpic Chairman Department of Agronomy UPCA, UPLB College Laguna E 109 Phillipines _ 72_ Dr. Antonio Diaz Chavez Centro Nacional de Tecnologia Agropuecaria Santa Tecla El Salvador, Central America Dr. Guillermo Galvez Centro Internacional de Agricultura Tropical Apartado Aereo 67-13 Cali. Lolombia South America Dr. S. Q. Haque The University of the West Indies Faculty of Agriculture St. Augustine Trinidad l.es t Indies Dr. C. 1. Kes"ani Faculty of Agriculture & Forestry University of Dar-Es-Salaam Morogoro Tanzania Dr. P. N. Patel Division of Mycology and Plant Pathology IARI Ne,. Delhi-12 India Dr. N. G. Vakili Mayaguez Institute of Tropical Agricul ture P. O. Box 70 Mayaguez Puerto Rico 00708 Dr. R. J. Williams IlTA P.M.B. 5320 Ibadan, Nigeria Drs. J.M. Yohe and J.E. Wheeler Embrapa Instituto de Pesquisa Agropecuaria do Nordeste Caixa Postal 205 Racife, Brazil 

The international testing program: aims, progress and problems seen from IITA

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The international testing program: aims, progress and problems seen from IITA

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