I am growing some tomato plants in a polytunnel (first year) and one of them seems to have developed a problem. The leaves at the top have become rather crispy and shrivelled. The rest of the leaves seem to be fine albeit slightly leathery. None of the other plants have this problem and seem to be growing well. I always keep the soil adequately watered but not soaking wet.I gave it a feed about 2 weeks ago when the flowers started appearing and it looked in really good condition at the time. As you know the weather recently has been quite cold so I was wondering if the temperature fluctuations could have had an adverse effect. Someone has also suggested possible damage to the roots.