panorama apparent angles

What you need it to render the panorama using a rectilinear projection. This is limited to scenes that span less than 180° but since those trees are 90° appart can do it, but will need more photos that cover the space between those trees.

With the frames you have, if you project as rectilinear, the panorama will have a ⋂ shape with trees on both sides but nothing in between. By taking extra images or at least shooting at a lower angle or from a lower position, you will capture the ground that would get projected between the trees.

Here's the problem. You want to show something that is close to being on either side of you (the trees in the row closest to the road) and display that on a flat display medium (screen or print, it doesn't matter) that is in front of you sufficiently that the extreme edges of the image are not on either side of you.

Short of displaying the result on a circular medium such as an IMAX screen that wraps 180° around the viewer, so that the extreme edges of the display medium are at the same angles to the observer's eyes as the items in the scene were to the camera's lens the easiest solution is to back up significantly and use a much longer focal length. A higher camera position that points down at a greater angle might also be helpful. Of course the change in perspective will also affect the relationships of all the other rows and columns in the orchard.

If you warp the projection to straighten the line along the road, the relative sizes of the trees will no longer look natural. In fact, some of the closest trees near the left and right edge of the image will look larger on their outside half than on their inside half.