Worldwide Dissemination and Importance of the Root-knot Nematodes, Meloidogyne spp. r J. N. SASSEW Abstract: Root-knot nematodes are widely distributed throughout the world. Their distribution and economic importance are purported to be related to biological and environmental factors favorable 1o Meloidogyne spp. A scheme for comparing Meloidogyne spp. with two other genera of diverse biological characteristics is presented to support this hypothesis. It is further suggested that a probability index can be developed to predict the likelihood of a given nematode species being transported, established, and becoming economically important ill regions of the world where it does not already occur. Key Words: root-knot nematodes, Meloidogyne spp., distribution. Root-knot nematodes of the genus phts M. ovalis (22), M. carolinensis (7), M. Meloidogyne are more widely distributed thamesi (2), M. naasi (9), M. ottersoni (27, throughout the world than any other 28), M. graminis (25, 28), and M. gramini- major group of plant-parasitic nematodes. cola (12), are known to occur in the United Furthermore, when their importance is States. Meloidogyne incognita, M. javanica, considered on a worldwide basis, they rank M. arenaria, M. hapla, and M. graminis high on the list of animate pathogens are widespread in the United States, al- affecting the production of economic plants. thongh distribution varies with species. The If one assumes that these two observations other species known to occur in the United are true, certain biological characteristics States are more host specific, a factor which and environmental influences favorable to may account for their limited distribution. Meloidogyne spp. must account for their For example, M. carolinensis has been wide distribution and economic importance. reported only fi'om blueberry in eastern Information concerning distribution of North Carolina; M. ottersoni from Canary described species of Meloidogyne is pre- grass, Wind Lake area, Wisconsin; M. ovalis sented, but no attempt is made to indicate from maple in Wisconsin; M. graminicola countries in which each species occurs. on grasses in Louisiana; and M. naasi on More importantly, biological characteristics various gramineae from California, Illinois, of nematodes which influence successful Oregon, Kansas, and Maryland. dissemination and establishment in a new Twenty-four additional species, which environment are discussed. are lesser known and of more restricted In any discussion about root-knot distribution, were described or first reported nematodes, one can separate the species from other continents or regions of the into two categories: (i) the most common world. The most common and well-known and well-known species, Meloidogyne species in the United States, indicated in incognita, M. iavanica, M. arenaria, and parenthesis, also occur in most other M. hapla, included in Chitwood's 1949 continents or regions. revision of the genus (1); and (ii) the less Central and South America: Meloido- widespread species, most of which were gyne exigua (11, 18), M. coffeicola (19), M. described later. lordeUoi (21), M. inornata (17), M. bauru- Since 1949, additional species have been ensis (16), (M. incognita, M. javanica, M. described from the United States and from arenaria, and M. hapla). other parts of the world so that approxi- Africa: M. africana (29), M. acronea (3), mately 35 are now recognized (6). Of these, M. kikuyensis (4), M. ethiopica (30), M. 11, including those species listed previously decalineata (30), M. megadora (30), M. otei[ae (5), (M. incognita, M. javanica, M. Received for publication 7 June 1976. arenaria, and M. hapla). 1Journal Series Paper No. 5118 of the North Carolina Agricultural Experiment Station, Raleigh 27607. Sym- India: M. indica (30), M. lucknowica posium paper presented at the joint annual meetings of (24), M. brevicauda (15), (M. incognita, M. the Society of Nematologists and the American Phyto- pathological Society, Houston, Texas, U.S.A. 10-14 August arenaria, M. javanica, M. graminicoIa, and 1975. M. hapla). M. brevicauda occurs in Sri 2 Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27607. Lanka (Ceylon) where it was first reported. 26 Dissemination of Meloidogyne spp.: Sasser 27 England: M. artiellia (8), M. naasi (9), influence the chances of successful dissemi- M. ardenensis (23), and O ¢. hapla). nation and establishment of a nematode Remainder of Europe and the Mediter- species and the likelihood that it will be- ranean region: M. deconincki (5), M. come economicaly important. From the litoralis (5), M. naasi, (M. incognita, M. known facts, we should be able to predict javanica, M. arenaria, and M. hapla). the probability that a particular species of Russia: M. hirjanovae (26), M. megrien- nematode can compete in all three phases sis (6), and M. tadshikistanica (14), (M. by placing numerical values on factors incognita). influencing distribution and establishment. Japan: M. mali (13), (M. hapla, m. For example, if we rate each biological or ]avaniea, M. incognita, and M. arenaria). environmental factor on a scale of 0-10, Southeast Asia, Australia, Fiji Islands: with 0 being most unfavorable and 10 being No new species described. (M. incognita, M. most favorable, an index of success could javanica, and M. arenaria). be estimated. In Table 1, M. incognita is Canada: M. microtfla (20), (M. hapla compared with two other nematode species and M. incognita). which represent very diverse characteristics Of the lesser known species described within the parameters considered. outside the United States since 1950, only" In the hypothetical scheme presented in M. naasi has been reported as occurring in Table 1, some factors should probably be the United States. Thus, despite very active given more weight in a formula than investigation in many parts of the world, others. This adjustment could be done only five or six cosmopolitan species have rather easily. Also, any one of several been found. Yet, all of these seem to have factors could impede or stop the process. the same biological characteristics, except Therefore, in the development of a formula possibly limitation of host range. A closer for predicting the likelihood of all three look is necessary. phases being completed, a built-in value or A comparison of Meloidogyne spp. with constant has to be inserted. Values given two other genera of diverse biological are subjective and vary among individuals characteristics may illustrate and support making the ratings. In spite of these limita- the hypothesis that distribution and eco- tions, a formula or index can be devised nomic importance of a given nematode can which would enable scientists to predict he explained on the basis of biological with a reasonable degree of accuracy the advantages or disadvantages and environ- relative probability of spread and establish- mental influences. If this can be done, there ment among many nematode groups and is reason to believe that a formula or index species. It seems reasonable that the genus can be developed which would help predict Meloidogyne is widely disseminated and whether or not a particular nematode pest economically important because of the high is likely to spread and become important in ratings reflected for several of the key areas where it does not already occur. For factors in the "establishment" and the "'eco- convenience, consideration will be given to nomically important phases." Anguina each of three phases as follows: (i) dis- tritici has a higher value for the "in transit" semination of live developmental stages of phase but lesser values than M. incognita a nematode species from one part of the for the "establishment" and "economic world to another, (ii) successful establish- importance" phases. Belonolaimus longi- ment in a new location, and (iii) conditions caudatus would rank third among these or factors favoring the likelihood that the three genera in the likelihood of being introduced species would develop to the transported and becoming established in a point of becoming an economically im- new environment. This fact can be attrib- portant pest. It is important to realize also uted to its ectoparasitic life habit, low that the first phase can occur without the reproductive rate, specific soil requirements, second, and that the first two phases can and perhaps other factors. occur without the third. A problem emerges There are many nematode species which in a new area only when all three phases are not widespread but which have the are completed. potential of becoming economically im- The factors shown in Table 1 obviously portant should they be transported to 28 Journal of Nematology, Volume 9, No. 1, January 1977 TABLE 1. Some factors which influence successful dissemination, establishment, and economic importance of a parasitic nematode. Probability Index" Meloidogyne Belonolaimus Anguina Biological and/or Environmental Influences incognita longicaudatus tritici In transit phase 1) Endo-/or Ectoparasite 6 3 10 2) Developmental stage(s) involved in transit 6 3 10 3) Amount of inoculum and frequency of transport 10 1 10 4) Type and condition of carrier--soil, fleshy root, seed, or leaves 6 3 10 5) Sensitivity to desiccation 3 2 10 Establishment phase 1) Number and relative suitability of available hosts 10 8 1 2) Amount of inoculum and frequency of transport 10 1 10 3) Temperature requirements 7 4 6 4) Moisture requirements 7 6 5 5) Soil requirements 7 1 9 6) Mode of reproduction 10 2 5 7) Survival mechanisms 3 3 1 8) Capacity to change and adapt to new situations and cultivars 5 1 1 Economic importance phase 1) Host range and economic importance of crops attacked 10 2 1 2) Number of life cycles and reproductive capacity at prevailing environmental conditions 10 3 3 3) Pathogenicity 6 8 10 4) Ability to interact with other soil-borne pathogens in disease complexes 10 5 2 5) Cropping systems and land management practices ~Probability index--Scale of 0-10; 0= highly unfavorable; 10=highly favorable. certain parts of the world.