Nicaraguan farmers have for a long time struggled with tomato production. The primary
problem has been Begomovirus infection, which devastated the tomato production in
the country in the 1990’s. In the battle against the Begomovirus other problems in the
native tomato production have been neglected. The overall goal with these projects was
to identify common tomato diseases and to evaluate their effect on yield and quality of
the tomato fruits at different nitrogen levels. This report contains two separate theses
(chapter 2 and 3). The results of the studies are based on the same field experiments. To
increase the understanding about local farming conditions (chapter 1), interviews were
made at two locations. During the interviews the farmers were asked questions about
the farms, their production and pesticide use. Today, the farmers overuse chemical
products to control different pests. The Nicaraguan farmers in general have a strong
belief that pesticides are the solution of all their agricultural problems.
The thesis in chapter 2 deals with the effect of nitrogen on some diseases of tomato. The
symptoms that appeared in the field experiment indicated that the plants were not
infected by the suspected pathogens and lab results showed that symptoms on the plants
were caused by two other diseases: bacterial wilt and powdery mildew (causing agents:
Ralstonia solanacearum and Leveilulla taurica). The results showed that plants
fertilised with double the normal amount of nitrogen were significantly more resistant to
powdery mildew. There was also a significant difference between the varieties in
severity of powdery mildew. Regarding bacterial wilt the results are ambiguous, one of
the field experiments show no difference between the treatments but in the other
experiment there was a considerably higher rate of infection in the to highest levels of
nitrogen fertilisation. The aim of the study in chapter 3 was to evaluate the effects of
nitrogen fertilization on the yield and quality of the tomato fruits and to evaluate the
relations between the incidence of diseases and nitrogen fertilization on one hand and
fruit quality on the other. The harvest was divided in good (marketable) and bad (not
marketable) fractions. To evaluate the fruit quality, taste tests were carried out on the
two first harvests and laboratory analyses of acid (% titratable acids) and sugar content
(ºBrix) were measured on the second harvest. The results showed that the unfertilized
plots had significantly lower foliar nitrogen content. The total harvest levels of the
experiment were in similar range as the average harvest for the region (12-18 t/ha), but
the marketable fraction was only between 39 and 50 % of the total yield. In the taste
test, one of the varieties was significantly the most preferred variety, independent of
fertilizing level. The high not marketable fraction was probably due to poor pollination
and fruit set caused by high temperatures and heavy infections of ...