What is causing large white spots on my sweet basil seedling's leaves, and can the plant be saved?

Question

Several weeks ago, I put soil and sweet basil seeds into part of a plastic water bottle that I cut. I put one seed in each of the water bottles, and made a hole at the bottom of the bottles to allow excess water to flow out of the bottles. Both of the plants have been in the same exact environment since they germinated. They have never been outdoors. After germinating, both seedlings looked pretty similar until a couple of days ago. The leaves on one are becoming withered and contain white spots. It has gotten worse from one day to the next. Fearing that the container was too small for the roots, I transplanted the seedling into a large pot yesterday.

The first image is what it looked like when I was transplanting it. The other two images are what it looked like roughly 18 hours later. The leaves seem to be getting worse.

08/06/2019 Update: I have not had a chance to cut the pale parts of the leaves out, but I was able to take pictures of what the plant looks like now (24 hours after the last two pictures I uploaded) and I took pictures of the other plant that has been exposed to the same exact conditions (same amount of sun, same temperature, same amount of water, and soil from the same bag). I can't really tell if the problem is getting worse or not. Here are today's images of both the unhealthy looking plant, and the healthy looking one:

Answer 1

This appears to be leaf miners. Flies or moths lay their eggs in between the top and bottom skins of the leaves. The eggs hatch and the larva eat the inside of the leaf. This is usually a short period of time, a small window when this happens. The leaves as they are now are still making food for the plant. I'd cut off the white parts a bit.

Have you added or changed anything in the last week? Have you fertilized at all? Have you added anything to the soil?

This is about the right time to finally add fertilizer, a balanced fertilizer. Dr. Earth's All Purpose 5-5-5 using half the amount the directions direct.

What is the light source? Starts need to be started from seed in 1X2" cells or tiny tiny pots. Using only potting soil that has no fertilizer no water holding gimmicks added. As the plant grows and you start seeing the roots coming out of the drain hole it is time to up pot, transplant into a slightly larger pot of soil.

The next size up should be 3 to 4 inches in diameter. This is when your plant will need its first fertilizer, balanced fertilizer. When the roots show at the bottom of this pot's drain hole the next size up is 6". Which depending on where you live is a good final pot for basil.

Your intuition was good, just needed to plant your start in a 3 to 4" pot not this humongous one. You'll get root rot. Transplant this little guy into a 4" pot using just sterilized cheapo potting soil. Add a tiny bit of balanced fertilizer. Allow to dry out between waterings.

Pretty sure this is leaf miner damage and all it takes is ONE fly or a moth to deposit eggs beneath the skin of the leaf. And fly away. Leaf miners are only a little destruction for a short while. Let's get this guy healthy again and give him some quiet time. Then let's talk about the future. Cut the damaged or even bumpy parts of the leaves off. It looks like the larva have grown up and flown away.

tomato leaf leaf miners

beet leaf miner damage more leaf miner damage

leaf miner damage

Answer 2

I put my vote on that the soil does not have enough nutrients. What kind of soil are you using? Soil from the garden? Compost? Old soil?

I've always grown basil from seeds in small pots by the kitchen window and never added fertilizers. On the other hand, I always used compost. Never let them dry out. The soil should be moist all the time (not soaked though) and they like a lot of sun, but not direct sunlight. Good conditions would be behind a white piece of cloth in the window with a "compost" soil, nutrient enough to give the basil what it needs.