How to specify the actual x axis values to plot as x axis ticks in R

You’ll find the answer to your question in the help page for ?axis.

Here is one of the help page examples, modified with your data:

Option 1: use xaxp to define the axis labels

plot(x,y, xaxt="n")
axis(1, xaxp=c(10, 200, 19), las=2)

Option 2: Use at and seq() to define the labels:

plot(x,y, xaxt="n")
axis(1, at = seq(10, 200, by = 10), las=2)

Both these options yield the same graphic:

PS. Since you have a large number of labels, you’ll have to use additional arguments to get the text to fit in the plot. I use las to rotate the labels.