Several species of Phytophthora have been reported worldwide on the crown of seedlings and adult tomato plants: P. erythroseptica, P. citricola, P. capsici, P. cryptogea, P. nicotianae This last species is the most frequently described; it is particularly damaging in nurseries, and especially in soil culture after planting. Note that attacks are also observed on tomato rootstocks (intra- or interspecific), particularly in the southwest, used as an alternative to methyl bromide (figure 3).

Whatever the species of Phytophthora raging, the symptoms observed on the tomato are frequently the same: a blackish lesion with rather diffuse outlines, rather humid, gradually encircling the collar of seedlings (figures 1 and 2) or of adult plants ( Phytophthora crown and root rot ); on young plants, the stem may be more or less constricted in the affected area. A longitudinal section of the stem shows that the vessels underlying the chancre are more or less brown, even more visible when the rotten cortical tissues disintegrate and disappear locally. The observation of fruiting bodies (the sporangia) in the decomposed tissues of the neck makes it possible to confirm the involvement of a Phytophthora (figures 4 and 5).

Let us add that very often, before going up on the collar, the Phytophthora spp. have already more or less altered the Roots , causing damp brown lesions and more or less generalized rots.

Finally, let us remember that certain species also induce alterations on Fruits , rather circular, made up of more or less concentric brown rings ( buckeye rot ); this is the case with P. nicotianae (figure 6).

For more information about these fungi, you can consult the sheet Miscellaneous Oomycetes .