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Nematodes The nematode problem is the major one to be addressed. As a starter, nematologists should determine the varieties of the offending pests. Also, the relation between nematode resistance and temperature should be checked. (Recent research has shown that nematode-resistant tomatoes become susceptible as temperature rises.)

Although nematode-killing chemicals can be used to treat the soil, these tend to be toxic and expensive. An alternative approach could be biological control.9 Screening for strains resistant to nematodes (and viruses) seems promising as well, although development of horticulturally viable types could take years.

Alternative approaches include the following:

  • Hybridizing naranjilla with closely related, nematode-resistant species. Hybrids with Solanum hirtum and S. macranthum, for example, have good nematode resistance. Backcrossing these to naranjilla has produced a range of plants that have shown resistance and have borne fairly good fruit.10

  • Grafting naranjilla on related plants with nematode-resistant rootstock. When cleft grafted on species such as S. macranthum and S. mammosum, naranjilla plants have survived for about three years and fruited successfully. In tropical Africa, naranjilla has done well when grafted to its nematode-resistant local relative, S. torum. 11

  • Improving plant vigor by better management.

  • Producing the crop in beds of sterilized soil.

  • Growing a cover crop or rotation crop of plants, such as velvet bean or Indigofera species, that help eliminate nematode infestations.

  • Inducing somaclonal variation in regenerated plants as a way of unmasking inherent nematode resistance that is now hidden.

  • Educating farmers about nematodes and the means of keeping sites free of infestation. (This is important, whatever other approach may be used.)


Botanical Name Solanum quitoense Lamarck

Family Solanaceae (nightshade family)

9 For example, the bacterium Pasteuria penetrans has proved as effective as current nematocides on other crops in Britain. Spores can be produced in vivo on nematodes in roots, without the necessity of sterile production systems. Information from B.R. Kerry.
10 Information from L.E. Lopez J.
11 Both hybridizing and grafting also bestow resistance to root and collar rot. However, further evaluation is needed to ensure that alkaloids in the fruits do not rise to hazardous levels. Information from J. Soria.

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