Heat stress in raspberries, part 2

So, many of you are probably thinking "Why would anyone try to grow raspberries in a hot, humid environment like North Carolina?" Well, you are not the only one that has had that thought. There are several points that I want to make in regard to this idea.

First, North Carolina has multiple environments. The three primary regions are the Coastal Plain, Piedmont and the Mountains.  So, within the state we have a range of elevations from sea level to over 3000 ft (ca 1000 m). This allows us to grow our plants in a wide range of environments.  In the summer, all regions are hot, some are just not as hot, with high temperatures only in the 80's. However, this range of climates allows some growers to produce fruit earlier in the season and some can go later in the season. We are not trying to produce raspberries in the coastal plain in mid July. That is just too hot for this delicate fruit.

Second, in warm conditions, fruit set is often a problem. However, in our screening process, we find that some of our test plants that are able to survive the heat and have flowers that can produce fruit.  And it is this last group that we choose to select and propagate for further observations. 

Third, even if a raspberry variety can survive in the hotter areas, we find that fruit size improves when we move it to our more moderate locations (see example of fruit size above). The two pictures are fruit from the same selection planted in two different places. The hotter location is SH (the Sandhills) and Sal (Salisbury) is only 90 miles away. 

Lastly, we are finding, thanks to Dr. Penny Perkins-Veazie, that even though some of the newer varieties look good at harvest, once we pick them they go downhill rapidly. Amazingly, the test plants from our program always seem to do better. 

The role of the environment on the performance of a variety is huge. In fact plant breeders spend alot of time evaluating GXE (Genotype X Environment) interactions. We know that the environmental influence on raspberry performance is significant and that our hot and humid climate enables us to screen in an environment that is not ideal for most raspberry varieties. But we are trying and think we are making good progress.