tomato seedlings: growth causes leaf drop

Asked April 7, 2014, 11:31 PM EDT

These are 'colossus', a rootstock I chose for its resistance. I'd hoped to learn grafting this year. The plants are 3-4 weeks old. There's a history: 1) first year using rockwool media, 2) they were allowed to get very hot during germination (80 degree room temp AND the warming mat was on for two days -- my mistake). I thought that I'd damaged them as there was little consistency in growth and a few leaves had fallen off. Then, about two days ago, I noticed light spots on the leaves. A slight movement of the tray can cause affected leaves to fall off.

What is this, can it be fixed, are my other plants---what were to be the scions--likely to have this problem?

Any help would be much appreciated.

mc

Arapahoe County Colorado fruits and vegetables

1 Response

Although more prevalent in soils, your photo suggests that seedlings may have developed a fungal disease called damping off (Pythium). Seedling stems become browned and "pinched". Stems may fall over and leaves drop or die.

The strange leafspots may be edema.
The most common cause of edema is the presence of abundant, warm water and a cool, moist atmosphere. Under these conditions roots absorb water at a rate faster than is lost through transpiration. Excess water accumulates in the leaf, some parenchyma cells enlarge and block the stomatal openings through which water vapor is normally released from the plant; thereby contributing to further water retention in the leaf. As cells divide, they take on a raised, corky, gall-like appearance.