Bernardita Sallato talks about a two-year project on root growth differences between WA 38 trees grown on G 41 and M9-Nic 29 rootstock and possible relation with green spot development.
Acknowledgment: Pom Club for organizing the meeting and Garret Bishop, GS Long, for moderating the Q&A.
Text Transcript and Description of Visuals
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| My name is Bernardita Sallato and I’m a tree fruit extension specialist at Washington State University. | Bernardita appears on screen in a video call along with her contact information and title. |
| So, first of all, the WA38 trials, or Cosmic. The Cosmic apple trials we’ve done most of them at the Roza farm in Prosser. You may know this, but it was planted in 2013 with the purpose of evaluating a pruning system, training system, and rootstocks. So we have randomized two different rootstocks, the M9 Nic 29 and the G41, and we have three training systems: the spindle, planted 12 by 3 in V-trellis. And those are double line planted at 12 also by one and a half foot apart over the row. And we have the bi-ax which is 10 by 3. So it’s a very neat place for us to do research because it’s randomized in terms of the root stocks, and also one of the oldest blocks that we have with the Cosmic apples. | Slide titled “WA 38” contains a photo of an apple research orchard. The trees are trained on trellises in long rows. |
| So before I move on to all the results and trials, I need to thank my research assistant, Juan Munguia. He is a former student of Oregon State University, and now he is my research assistant and he’s applying for doing a masters with Washington State University. He’s been a tremendous help for all my trials. I also, for the WA38 trials, have a lot of support from growers, especially from Blyhl that manage all the IPM and Burrows Tractor, with Tyler that allows us to harvest the fruit like you see here in this bin. | Slide contains a photo of Juan Munguia, a large bin of apples, and the logos of the two mentioned companies. |
| Okay, so the first trial I want to talk about is a root growth difference between the M9 Nic 29 and G41. We did this by placing what we call the root windows in the ground for three replicates per rootstock. So this way we evaluate when the roots start growing, the period of growth, and also overall growth between those two root stocks. | Slide titled “Root growth differences” shows two horizontal soil profile images. The top image, labeled G41, contains many visible roots of varying thickness. The bottom image, labeled M9, shows fewer roots within the soil. |
| One thing that we’ve been monitoring with the root growth, of course, are the conditions in the soil and temperature–which is one of the most important for root growth– and moisture, and we try to correlate that with the stage of development of the plants. | A line graph titled “2019” shows temperature in degrees Fahrenheit from April to October. The red line rises from spring into summer, peaks mid summer, and declines into fall. |
| So here you see the result from 2019, where the roots start growing at this stage for G41. We have two peaks of growth. The first one started around May 3rd. We had the bloom time pretty much at the same time that we had the first root tip. | Two black markers labeled “G41” appear on the graph, pointing to the stages in which there was a peak in root growth for this variety. |
| For M9 in 2019, it had about two week delay in terms of root growth, the first roots. So it was a little bit delayed compared to the G41, and did not show a second peak of growth during the fall. | A blue marker labeled “M9” appears on the graph, pointing to the peak of root growth for this variety. |
| Now in 2020, this is the other line that you see here. The temperatures were not too different, especially at the beginning of the year, but we did observe that we got a bit warmer soil earlier compared to 2019. | An additional line appears on the graph representing the results from 2020. |
| And what happened is that we see a little bit of a shift in the growth. So M9 actually start growing earlier under these conditions, earlier than G41. Both started growing at like a month after full bloom, and both rootstocks showed a second peak of growth in the fall. M9 was a little bit small while G41 grew from around September to October, was still growing. | The black and blue markers are shifted so that the peak in root growth for M9 is before the peak for G41, and an additional marker is added for M9 later in the season. |
| Overall, what we conclude with this research–but also relying on data that we have researched from other plants, even cherries and apples–is that consistently, there is a requirement of the stage of the plant, but also temperature is really important for first root growth, especially early in the spring. So we see that we require temperatures above 59 degree Fahrenheit, which is around 15 degrees Celsius, for the first routes to grow. | |
| Now, what does it means in terms of vigor and the difference between these two root stocks? We observe here, this is the accumulated growth. In this line here, you have the accumulated growth in centimeters compared between the two root stocks. So you can see that in 2019, they both started at pretty much the same time. There were no differences between the two rootstocks, but then M9 grew for about a month and then stopped growing and stayed kind of the same. And actually there is a death of roots in this period. While the G41 had a much faster rate of growth, but also continue growing for more than a month. This makes a big difference in terms of the volume of roots that we see active for these two different root stocks | A bar graph titled “2019” shows root growth in centimeters from mid-May to late June. Red bars represent G41 and grey bars represent M9. Root growth increases over time for both by G41 is consistently much higher than M9. M9 also shows stagnation in growth starting in early June. |
| Now I want to show this information, because later I’m going to relate this to green spot. What I want to show here is that, in 2019 in the V-trellis, we had 14 percent green spot in the M9 Nic 29, and 55 percent green spot in the G41. I want you to remember that this block is a very fertile block. We have high vigor, it’s a silt loam soil, so it’s not like a sandy soil, for example, that you will you might have in the Mattawa area or Sunrise. | An illustration of an apple with green spot and the two mentioned percentages appear on screen. |
| In 2020 what we observed is that, M9 and G41, again they were very similar in growth. This year, there was less growth overall. A similar M9, and both grew pretty much the same, but the G41 had a lesser growth in 2020. We’ve been working on managing the vigor in this variety in our site. The other thing that we observed, is that even though M9 started growing earlier and faster, the G41 kind of caught up on the growth. It had a speed growth later in the summer and grew for longer period of time. And like I showed before, it also had a second peak of growth in October. | A bar graph titled “2020” shows root growth in centimeters from late April to late October. Red bars represent G41 and grey bars represent M9. Root growth increases over time for both with similar rates seen for both varieties. |
| The second year, we had a reduced level of green spot of three percent in M929 in the V-trellis, and ten percent in the G41. | An illustration of an apple with green spot and the two mentioned percentages appear on screen. |
| The biggest difference between these two rootstocks is also the crop load. I cannot separate vigor with crop load. So, for me, this is an indication of vigor. The M9 has less vigor, and also in terms of shoot growth, but it has more crop load. It has bigger and more fruit compared to the G41 that has more shoot growth and less crop load. Now the size of each fruit are had no difference. They were not significantly different. | A bar graph titled “Fruit per tree” compares M9 and G41. M9 trees have substantially more fruit per tree than G41. |
| So then we get to this idea of thinking about the importance of vigor management, and how that can lead to calcium related disorders. Or really, any kind of disorders, like the one we I’m going to talk about later, the green spot. So what I want to show here, is these three different systems. This is data collected from different trees, and the statistical analysis is within systems. Everything involved is significantly different between the two rootstock, which is the only thing we have randomized in the block. So as you can see here, the spindle system in which we have more vigor and more green spot, shown at the bottom here. This one had an estimated bins per acre of 56 and 45 for M9 and G41 respectively. And those also have very high levels of green spot, 29 percent for M9 and 45 percent for G41. Now if we see and compare with the other systems that are less vigorous, we also have a different amount of fruit per tree, with G41 having less fruit, but also more vigor more shoot growth. Sizes are not different statistically, and the green spot levels in M9 is reduced to 14 compared to 55 in G41. | Slide titled “Green Spot 2019” shows three illustrations of apple tree structures comparing M9 and G41 rootstocks. Below, a table compares M9 and G41 across three examples for fruit per tree, fruit weight, yield, and percent green spot. |
| Then finally, the favorite for the Roza block, at least, is the bi-ax, which is absolutely a less vigorous system for us. You can see that with the amount of fruit. We have more crop load in this system, and again, you can see a very acceptable levels of green spot. This is green spot at harvest. So we collect all the fruit from the tree to evaluate these levels of green spot. So we had one percent for M9 Nic 29 and 18 for G41. So this relates the disorder with the fact that the vigor plays a very important role, but also there is a difference between–despite the system–there is a different between the root stocks. | |
| One of the questions I have is for you, Bernardita. On comparing the root growth the one year in 2019, you had the M9 just in the spring but not in the fall, and then the following year, you saw it in the spring and the fall. What are your thoughts on that what might cause the difference? | The name of an attendee appears on screen as the question is asked. |
| That’s a good question, and I think that no one really can answer that with 100 percent certainty. There is a big variability on root growth depending on the soil conditions and the tree condition in general. so one thing that we do know is that the M9–and I think I’m going to share that in another slide maybe–there was a work done in the 50’s that showed that the M9 is susceptible to high temperatures in the soil. So we think that maybe the there were some effects in terms of the temperature and the stress conditions for M9. Sometimes you kind of kill the roots and then that triggers new growth later. It is normal though, at least from what I learned when I was in university. That it is more normal to have those two peaks of growth, and I would think that, when you don’t have adequate conditions is where you don’t see that second peak of growth. And that could be temperature. Heat stress, water and nutrition also have shown to be an important factor for root growth. Also if you have lack of nitrogen or other nutrients in the soil, you also won’t see that second root growth. | Bernardita appears full screen. |
| So again, if you have more questions and you want to reach out to me, you have my email contact there and also you can find me in WSU Tree Fruit Extension. | A conclusion slide containing a photo of a diseased apple along with the author’s contact information appears on screen. |
