Q.Paw Paw Tree Leaves Going Yellow.
I have a small paw paw tree (about 1m high) in a pot I put it in a larger pot after buying it in autumn and through the winter it’s leaves were dying from the base to the tip and from the bottom leaves to the top. I had it sheltered from the frost as I do not live in the tropics, I moved it out into full sun in spring and sprayed with wettable sulfur and it started to really recover and grow well. Its leaves were growing big and were really green then as summer came the leaves started to turn yellow from the base (where it attaches to the stem) to the tip (and formed brown dead patches in the leaves) and the leaves died. It did this on the bottom leaves steadily working its way up to the upper leaves. Is this a disease or nutrient deficiency or watering problem, I water every second day as temperatures here are 38c to high 40s (100f to 117f) in summer.

Certified GKH Gardening Expert
I had to look up your tree since it didn't look like the paw paw trees I'm familiar with. Apparently in Australia you refer to papaya trees as paw paws. Young papaya trees need fertilizer every two weeks. They also need well drained soil to prevent stem rot.
Here is more:
https://www.gardeningknowhow.com/edible/fruits/papaya/growing-papaya-fruit.htm
https://www.gardeningknowhow.com/edible/fruits/papaya/papaya-stem-rot-treatment.htm