Intercropping, the simultaneous cultivation of multiple crop species, has been used throughout history and remains common among farmers of small landholdings in the tropics. One benefit of this practice may be disease control. In phenomenological research comparing disease in monocrops and intercrops, primarily due to foliar fungi, intercropping reduced disease in 73% of more than 200 studies. Nematodes are the primary pathogen for which disease increases are reported, but variability in disease impacts among studies can be high for all types of diseases. The mechanisms by which intercrops affect disease dynamics include alteration of wind, rain, and vector dispersal; modification of microclimate, especially temperature and moisture; changes in host morphology and physiology; and direct pathogen inhibition. The effect of intercropping on host density is a factor underlying many of these mechanisms. By synthesizing our growing understanding of mechanisms and their interactions with phenomenological studies, we may develop a theoretical grounding that allows us to improve the application of intercropping for tropical smallholders and industrial farmers alike.

Diseases in Intercropping Systems

Tomato (Solanum lycopersicum) crops can be severely damaged due to parasitism by the root-knot nematode (RKN) Meloidogyne incognita, but are protected when intercropped with crown daisy (Chrysanthemum coronarium L.). Root exudate may be the determining factor for this protection. An experiment using pots linked by a tube and Petri dish experiments were undertaken to confirm that tomato-crown daisy intercropping root exudate decreased the number of nematodes and alleviated nematode damage, and to determine crown daisy root exudate-regulated nematode chemotaxis. Following a gas chromatography-mass spectrometry assay, it was found that the intercropping protection was derived from the potent bioactivity of a specific root exudate component of crown daisy, namely lauric acid. The Mi-flp-18 gene, encoding an FMRFamide-like peptide neuromodulator, regulated nematode chemotaxis and infection by RNA interference. Moreover, it was shown that lauric acid acts as both a lethal trap and a repellent for M. incognita by specifically regulating Mi-flp-18 expression in a concentration-dependent manner. Low concentrations of lauric acid (0.5-2.0mM) attract M. incognita and consequently cause death, while high concentrations (4.0mM) repel M. incognita. This study elucidates how lauric acid in crown daisy root exudate regulates nematode chemotaxis and disrupts Mi-flp-18 expression to alleviate nematode damage, and presents a general methodology for studying signalling systems affected by plant root exudates in the rhizosphere. This could lead to the development of economical and feasible strategies for controlling plant-parasitic nematodes, and provide an alternative to the use of pesticides in farming systems.

Lauric acid in crown daisy root exudate potently regulates root-knot nematode chemotaxis and disrupts Mi-flp-18 expression to block infection

The root-knot nematode (RKN) is one of the most damaging agricultural pests.Effective biological control is need for controlling this destructive pathogen in organic farming system. During October 2010 to 2011, the nematicidal effects of the Syncephalastrum racemosum fungus and the nematicide, avermectin, alone or combined were tested against the RKN (Meloidogyne incognita) on cucumber under pot and field condition in China. Under pot conditions, the application of S. racemosum alone or combined with avermectin significantly increased the plant vigor index by 31.4% and 10.9%, respectively compared to the M. incognita-inoculated control. However, treatment with avermectin alone did not significantly affect the plant vigor index. All treatments reduced the number of root galls and juvenile nematodes compared to the untreated control. Under greenhouse conditions, all treatments reduced the disease severity and enhanced fruit yield compared to the untreated control. Fewer nematodes infecting plant roots were observed after treatment with avermectin alone, S. racemosum alone or their combination compared to the M. incognita-inoculated control. Among all the treatments, application of avermectin or S. racemosum combined with avermectin was more effective than the S. racemosum treatment. Our results showed that application of S. racemosum combined with avermectin not only reduced the nematode number and plant disease severity but also enhanced plant vigor and yield. The results indicated that the combination of S. racemosum with avermectin could be an effective biological component in integrated management of RKN on cucumber.

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Efficacy Evaluation of Fungus Syncephalastrum racemosum and Nematicide Avermectin against the Root-Knot Nematode Meloidogyne incognita on Cucumber

The research explorations on the subject entitled “Status of Genus Meloidogyne Goeldi, 1892 in H.P. and its Management in Tomato (Solanum lycopersicum L.) and Capsicum (Capsicum annuum L.)” were undertaken to ascertain the status of Genus Meloidogyne Goeldi, 1892, in the state of Himachal Pradesh and to explore the possibilities of nematode management in highly susceptible Tomato and Capsicum crops utilizing environment and crop friendly tools of management and confining the use of chemical nematicides to nursery level. Faunistic incidence of plant parasitic nematodes with emphasis on species of Meloidogyne was conducted by collecting 586 soil samples from the vegetations covering all the four agro-climatic zones of the state. Samples when analysed in laboratory revealed the nematode genera viz., Meloidogyne, Helicotylenchus, Tylenchorhynchus and Pratylenchus in all the zones irrespective of climate conditions and altitude. The other nematode genera registering their presence only in mid hill zone in the specific crops were Hirschmanniella (rice), Hoplolaimus (citrus and sugarcane), Macroposthonia (citrus) and Hemicycliophora (guava). Four species of Genus Meloidogyne i.e., M. incognita, M. javanica, M. graminicola and M. arenaria were identified from different host crops on the basis of their morphological characters, perineal patterns of the female and morphometric measurements. Among these, the most prevalent with cosmopolitan distribution was M. incognita recorded from most of the districts falling in various agro-climatic zones, damaging vegetable, fruit and ornamental crops. This nematode completed one life cycle in 20 days on tomato at the temperature range of 25-28C. The incidence of M. javanica was confined to low altitude range of 322-478 m. a. s. l. Meloidogyne graminicola was found to infest cereals like rice, wheat and maize in the subtropical climate. Meloidogyne arenaria was recorded for the first time from okra and tomato in the mid hill region of the state. Among the nursery treatments tried against M. incognita, all the disinfectants viz. dazomet, formalin, carbofuran barring STTC and seed treatment with formulation of Pseudomonas fluorescens were found to be effective as evident from the healthy, ungalled roots and optimum aerial growth. Seedlings from dazomet treated nursery when root dipped in plant formulations prior to their transplantation in plots amended with neem or groundnut cake yielded best results in forms of plant growth parameters, fruit yield and reduction in nematode population and galling. Signature of Major Advisor Signature of Student Countersigned Professor and Head Department of Entomology & Apiculture Dr. Y. S. Parmar University of Horticulture & Forestry Nauni, Solan, H.P. -173230

STATUS OF GENUS Meloidogyne GOELDI, 1892 IN H.P. AND ITS MANAGEMENT IN TOMATO (Solanum lycopersicum L.) AND CAPSICUM (Capsicum annuum L.)

The pathogenic potential of Meloidogyne incognita on okra (Abelmoschus esculentus) was determined at initial population densities of 0, 1000, 2000 and 4000 second stage juveniles per kg of soil in pots in the glasshouse inoculated after 2 nd , 3 rd , 4 th and 5 th week of emergence. Significant reductions in plant height and fresh shoot weight and increases in root weight, number of galls and egg masses were observed at all inoculum densities. With an increase in inoculum level, there was a progressive increase in height and shoot weight reductions, root weight, number of galls and egg masses. Plants inoculated after 2 nd week of emergence were heavily damaged. However, with the increase in plant age at the time of inoculation, the damaging effects lowered significantly. Reductions in height and shoot weight and increase in root weight, number of galls and egg masses were found to be directly proportional to inoculum densities. On the other hand, with an increase in the initial inoculum density and plant age there was a corresponding decrease in the reproduction factor being inversely proportional to inoculum densities and plant ages.

Estimation of damage to okra (abelmoschus esculentus) by root-knot disease incited by meloidogyne incognita

Screening plants resistant against Meloidogyne incognita and integrated management of plant resources for nematode control

The invention discloses new use of lauric acid in prevention and control of meloidogyne incognita. According to the new use, the lauric acid is used for preparing a meloidogyne incognita insecticide; and in the insecticide, the lauric acid can be separately used as an active ingredient, and can also be compatible with other active ingredients for preventing and controlling the meloidogyne incognita to form an active ingredient. The insecticide is a methanol solution of the lauric acid, the insecticide is a repellent or an attractant, and the concentration of the lauric acid in the repellent is 4.00mM; and the concentration of the lauric acid in the attractant is 0.5 to 2.00mM. The methanol solution of the lauric acid used for preventing and controlling the meloidogyne incognita is safe, nontoxic and effective; when the concentration of a lauric acid solution is 4.00mM, the meloidogyne incognita can be repelled, and the lethality of the meloidogyne incognita is up to 67 percent; and when the concentration of the lauric acid solution is 0.5 to 2.00mM, the meloidogyne incognita can be attracted, and the lethality of the meloidogyne incognita reaches 39 percent.

Yuanmei Zuo

Papers

Screening plants resistant against Meloidogyne incognita and integrated management of plant resources for nematode control

New use of lauric acid in prevention and control of meloidogyne incognita